pH SENSITIVE CARRIER AND PREPARATION METHOD THEREOF, AND pH SENSITIVE DRUG AND pH SENSITIVE DRUG COMPOSITION EACH CONTAINING THE CARRIER, AND METHOD FOR TREATING OR PREVENTING DISEASES USING THE SAME

ABSTRACT

A pH sensitive carrier which includes at least one pH sensitive compound selected from the group consisting of deoxycholic acid, cholic acid, ursodeoxycholic acid, chenodeoxycholic acid, hyodeoxycholic acid, C27 bile acid, glycodeoxycholic acid, glycyrrhizic acid, glycyrrhetinic acid and salts thereof, and at least one amphipathic substance selected from the group consisting of a phosphatidylcholine having 10 to 12 carbon atoms, a polyoxyethylene sorbitan monofatty acid ester having 12 to 18 carbon atoms, a sorbitan fatty acid ester having 16 to 18 carbon atoms, glycerol monooleate, glycerol dilaurate, glycerol distearate, glycerol dioleate, polyoxyethylene castor oil and α-tocopherol, and which is capable of developing a membrane disruptive function promoting effect.

RELATED APPLICATIONS

This application claims priority to U.S. application No. 61/670,332filed on Jul. 11, 2012 and Japanese Patent Application No. 2012-124796filed on May 31, 2012, the entire contents of both of which areincorporated herein by reference.

TECHNICAL FIELD

Disclosed are a pH sensitive carrier and a preparation method thereof, apH sensitive drug and a pH sensitive drug composition each containingthe carrier, and a method for treating or preventing a disease using thesame. More particularly disclosed area pH sensitive carrier which isuseful for DDS (Drug Delivery System) and is capable of developing amembrane disruptive function promoting effect in response to a weaklyacidic environment, and a preparation method thereof, and a pH sensitivedrug and a pH sensitive drug composition each containing the carrier,and a method for treating or preventing a disease using the same.

BACKGROUND DISCUSSION

In recent years, extensive studies have been made on DDS carriers(carriers) for delivering a physiologically active substance to anintended site in a required amount. Attention has now been paid to astimuli responsive carrier from the standpoint of an improvement inaccumulation and the selection of the delivery site, and many reportshave been made on studies concerned with external stimulation with heat,a magnetic field or the like, and in vivo stimulation such as ofmolecular recognition, pH change, enzymatic reaction or the like. Amongthem, a carrier which is sensitive to a weakly acidic pH has beeninvestigated for a long time.

For instance, as a pH sensitive carrier responsive to a weakly acidicenvironment, there are known pH sensitive liposomes wherein varioustypes of pH sensitive elements such as PHC (Palmitoyl Homocysteine),oleic acid, CHEMS (Cholesteryl Hemisuccinate) and the like are added toliposomes containing PE (Phosphatidylethanolamine) (S. Simoes et al.,Adv. Drug Deli. Rev. 2004 56 947-965 and the like). Recently, there havebeen reported studies, for the purpose of enhancing function, on novelsynthetic materials such as PEAA (Poly(2-ethylacrylic Acid)), SucPG(Succinylated Poly(glycidol)) and the like, synthetic peptides such asGALA, pHLIP (pH Low Insertion Peptide) and the like, biodegradablematerials such as PLGA (Poly(Lactic-co-glycolic Acid)) and the like, andVLP (Virus Like Particle) and Virosome using a pH sensitive viralcomponent.

The pH sensitive carrier is expected to efficiently deliver aphysiologically active substance to a site such as of a tumor orinflammation where a pH lowers in a living body (Reshetnyak et al., PNAC2007 vol. 104, 19, 7893-7898) or to deliver to the cytosol by utilizingthe acidification of vesicles after being taken up by cells.

With respect to the delivery to the cytosol by using the acidificationof vesicles, it has been found that migration of a drug to the cytosolis facilitated by promoting membrane fusion of a carrier upon deliveryto endosomes, and a DDS carrier of a peptide derivative having a pHsensitive site whose structure is changed in response to the pH, amembrane fusion site and a transmembrane site has been reported inJapanese Patent Laid-open No. 2006-34211.

Such a delivery of a physiologically active substance to vesicles isutilizable in various fields and is thus a technique that is in demand.For instance, delivery of RNA or DNA to the cytosol enables genetherapy, and it has been expected to induce CTL (Cytotoxic T Lymphocyte)by the delivery of an antigen to the cytosol. The cytosolic delivery ofa low molecular weight anticancer agent has been reported as having animproved effect on activity, and its application to a novel type of drugfor use as an intracellularly targeted drug has been considered. Thecytosolic delivery of a physiologically active substance is a majorproblem to solve in these fields and is thus desirable.

In view of the fact that there is a successful case of delivering pHLIPhaving sensitivity to a pH of not higher than 6 to an acidosis site asdescribed in Reshetnyak et al., PNAC 2007 vol. 104, 19, 7893-7898 or apH arriving within endosomes in the vicinity of 4 as described in S.Simoes et al., Adv. Drug Deli. Rev. 2004 56 947-965, it is required thata pH-sensitive carrier have high sensitivity between neutral pH and a pHof 4. This is described in many documents. It is further important fromthe standpoint of practical use that the carrier is made of a safematerial.

SUMMARY

Many pH sensitive liposomes and biodegradable materials have a problemin that they exhibit sensitivity at too low a pH or have only aninadequate function. Moreover, with respect to a method of directlymodifying a pH sensitive material, there is a concern that the activityof a physiologically active substance can decrease. A novel type ofsynthetic material or a viral component would raise concerns from thestandpoint of safety.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1A is a schematic view of a drug including an illustrative pHsensitive carrier and a physiologically active substance supported withthe carrier.

FIG. 1B is a schematic view showing delivery of a physiologically activesubstance supported with a pH sensitive carrier to cellular cytosol as aresult of the development of membrane disruptive function promotingeffect of the pH sensitive carrier in case where a pH sensitive drug isused.

FIG. 1C is a schematic view showing delivery of a physiologically activesubstance mixed with a pH sensitive carrier to cellular cytosol as aresult of the development of membrane disruptive function promotingeffect of the pH sensitive carrier in the case where a pH sensitive drugcomposition is used.

FIG. 2A is a photograph of dispersions of deoxycholic acid and EYPC (EggYolk Phosphatidylcholine) wherein deoxycholic acid is contained atdifferent concentrations.

FIG. 2B is a photograph of dispersions of deoxycholic acid and DLPC(Dilauroyl Phosphatidylcholine) wherein deoxycholic acid is contained atdifferent concentrations.

FIG. 2C is a graph showing a transmittance of dispersions containingEYPC and deoxycholic acid.

FIG. 2D is a graph showing a transmittance of dispersions containingDLPC and deoxycholic acid.

FIG. 3 is a graph showing a zeta potential of a dispersion containingEYPC and deoxycholic acid in relation to the amount of deoxycholic acid.

FIG. 4 is a graph showing leakages of EYPC alone, DLPC alone,deoxycholic acid alone, EYPC-deoxycholate complex and DLPC-deoxycholatecomplex at different pHs.

FIG. 5(A) is a graph showing fluorescent intensity ratios of thedispersions of EYPC alone, DLPC alone, deoxycholic acid alone,EYPC-deoxycholate complex and DLPC-deoxycholate complex at different pHsin case of incubation with a double fluorescence-labeled liposome; andFIG. 5(B) is a graph showing fusion rates of deoxycholic acid alone,EYPC-deoxycholate complex and DLPC-deoxycholate complex.

FIG. 6 is a graph showing leakages of DOPE (DioleoylPhosphatidylethanolamine)-Chems liposome, DOPE-oleic acid liposome andDLPC-deoxycholate complex relative to the pH.

FIGS. 7(A) and 7(B) are, respectively, a graph showing fusion rates ofdeoxycholic acid alone, EYPC-deoxycholate complex and DLPC-deoxycholatecomplex in relation to the amount of deoxycholic acid.

FIG. 8(A) is a graph showing fusion rates of deoxycholic acid alone,DSPC (Distearoyl Phosphatidylcholine)-deoxycholate complex, DPPC(Dipalmitoyl Phosphatidylcholine)-deoxycholate complex, DMPC(Dimyristoyl Phosphatidylcholine)-deoxycholic acid complex,DLPC-deoxycholate complex and DDPC (DidecanoylPhosphatidylcholine)-deoxycholate complex; and FIG. 8(B) is a graphshowing fusion rates of deoxycholic acid alone, HSPC (HydrogenatedSoybean Phosphatidylcholine)-deoxycholate complex, DOPC (DioleoylPhosphatidylcholine)-deoxycholate complex and POPC (1-Palmitoyl 2-OleoylPhosphatidylcholine)-deoxycholate complex.

FIG. 9(A) is a graph showing leakages of deoxycholic acid alone, DLPE(Dilauroyl Phosphatidylethanolamine) alone, DMPE (DimyristoylPhosphatidylethanolamine) alone, DSPE (DistearoylPhosphatidylethanolamine) alone and DOPE alone; and FIG. 9(B) is a graphshowing leakages of deoxycholic acid alone, DLPE-deoxycholate complex,DMPE-deoxycholate complex, DSPE-deoxycholate complex andDOPE-deoxycholate complex.

FIG. 10 is a graph showing leakages of complexes of deoxycholic acidwith macromolecular materials at a pH of 5.0.

FIG. 11 is a graph showing leakages of complexes of EYPC, deoxycholicacid and DLPC or SPAN 85 at a pH of 7.4 in (A) and a pH of 5.0 in (B).

FIG. 12 is a graph showing leakages of complexes of DLPC and varioustypes of candidate compounds at a pH of 7.4 in (A) and a pH of 5.0 in(B).

FIG. 13 is a graph showing leakages of complexes of DLPC and varioustypes of candidate compounds relative to the pH.

FIG. 14 is a graph showing fusion rates of various types of pH sensitivecompounds when used alone in (A) and complexes of DLPC and various typesof pH sensitive compounds in (B).

FIG. 15 is a micrograph obtained in case where a fluorescence-labeledDLPC-deoxycholate complex and HeLa cell are incubated in media of a pHof 7.4 in (A) and a pH of 5.3 in (B), and also shows a fluorescenceintensity of the cells evaluated by use of a flow site meter in (C).

FIG. 16 is a graph showing leakages of carriers incorporating a peptidein (A) and a protein in (B) at pHs of 7.4 and 5.0, respectively.

FIG. 17 is a graph showing fusion rates of DLPC-deoxycholate complexesin (A) and DLPC-ursodeoxycholate complexes in (B), both incorporatedwith a peptide and a protein, respectively, at pHs of 7.4 and 5.0.

FIG. 18 is a photograph of (A) a solution of a fluorescence-labeledpeptide alone, (B) a solution of fluorescence-labeled peptide-containingDLPC alone, (C) a solution of a fluorescence-labeled peptide-containingDLPC-deoxycholate complex, and (D) a solution of a fluorescence-labeledpeptide-containing DLPC-ursodeoxycholate complex.

FIG. 19 is a fluorescence micrograph of cells treated with afluorescence-labeled peptide alone in (A), a fluorescence-labeledpeptide-containing DLPC alone in (B) and a fluorescence-labeledpeptide-containing DLPC-deoxycholate complex in (C).

FIG. 20 is a micrograph in (A) and a fluorescence micrograph in (B) ofcells treated with a fluorescence-labeled peptide-containingDLPC-deoxycholate complex, and a micrograph in (C) and a fluorescencemicrograph in (D) of cells treated with a fluorescence-labeledpeptide-containing DLPC-ursodeoxycholate complex, respectively.

FIG. 21 shows the results of evaluating delivery of β-gal to cellularcytosol and particularly, the results of evaluation on β-gal alone in(A), β-gal-containing DLPC-deoxycholate complex in (B) andβ-gal-containing DLPC-ursodeoxycholate complex.

FIG. 22A shows the results of a test of checking the delivery tocellular cytosol when the respective pH sensitive carriers andphysiologically active substances are independently used and are,respectively, superposed images of micrographs and fluorescencemicrographs obtained by using, in a cell culture environment, of (A)fluorescence-labeled peptide-FITC alone, (B) fluorescence-labeledOVA-FITC alone, (C) a combination of fluorescence-labeled peptide-FITCand EYPC-deoxycholate complex, (D) a combination of fluorescence-labeledOVA-FITC and EYPC-deoxycholate complex, (E) a combination offluorescence-labeled peptide-FITC and DLPC-deoxycholate complex, (F) acombination of fluorescence-labeled OVA-FITC and DLPC-deoxycholatecomplex, (G) a combination of fluorescence-labeled peptide-FITC and SPAN80-deoxycholate complex, (H) a combination of fluorescence-labeledOVA-FITC and SPAN 80-deoxycholate complex, (I) a combination offluorescence-labeled peptide-FITC and DDPC-deoxycholate complex, and (J)a combination of fluorescence-labeled OVA-FITC and DDPC-deoxycholatecomplex.

FIG. 22B shows the results of a test of checking the delivery to cellcytoplasm when the respective pH sensitive carriers and physiologicallyactive substances are independently used and are, respectively,superposed images of micrographs and fluorescence micrographs obtainedby using, in a cell culture environment, of, (K) a combination offluorescence-labeled peptide-FITC and PEG-10 castor oil-deoxycholatecomplex, (L) a combination of fluorescence-labeled OVA-FITC and PEG-10castor oil-deoxycholate complex, (M) a combination offluorescence-labeled peptide-FITC and Tween 20-deoxycholate complex, (N)a combination of fluorescence-labeled OVA-FITC and Tween 20-deoxycholatecomplex, (O) a combination of fluorescence-labeled peptide-FITC andTween 80-deoxycholate complex, (P) a combination of fluorescence-labeledOVA-FITC and Tween 80-deoxycholate complex, (Q) a combination offluorescence-labeled peptide-FITC and α-tocopherol-deoxycholate complex,(R) a combination of fluorescence-labeled OVA-FITC andα-tocopherol-deoxycholate complex, (S) a combination offluorescence-labeled peptide-FITC and DLPC-ursodeoxycholate complex, and(T) a combination of fluorescence-labeled OVA-FITC andDLPC-ursodeoxycholate complex.

FIG. 22C shows the results of a test of checking the delivery to cellcytoplasm when the respective pH sensitive carriers and physiologicallyactive substances are independently used and are, respectively,superposed images of micrographs and fluorescence micrographs obtainedby using, in a cell culture environment, of, (U) a combination offluorescence-labeled peptide-FITC and DLPC-glycyrrhizic acid complex,(V) a combination of fluorescence-labeled OVA-FITC and DLPC-glycyrrhizicacid complex, (W) a combination of fluorescence-labeled peptide-FITC andDLPC-chenodeoxycholate complex, (X) a combination offluorescence-labeled OVA-FITC and DLPC-chenodeoxycholate complex, (Y) acombination of fluorescence-labeled peptide-FITC andDLPC-hyodeoxycholate complex, (Z) a combination of fluorescence-labeledOVA-FITC and DLPC-hyodeoxycholate complex, (AA) a combination offluorescence-labeled peptide-FITC and DLPC-glycodeoxycholate complex,and (AB) a combination of fluorescence-labeled OVA-FITC andDLPC-glycodeoxycholate complex.

DETAILED DESCRIPTION

Accordingly, an illustrative aspect provides a pH sensitive carrierwhich can serve as a carrier for physiologically active substance and isable to develop a membrane disruptive function promoting effect inresponse to a weakly acidic environment and its preparation method, andalso provides a pH sensitive drug and a pH sensitive drug compositioneach containing the carrier, and a method for treating or preventing adisease using the same.

Disclosed are the following illustrative aspects.

-   -   (1) a pH sensitive carrier which includes at least one pH        sensitive compound selected from the group consisting of        deoxycholic acid, cholic acid, ursodeoxycholic acid,        chenodeoxycholic acid, hyodeoxycholic acid, C27 bile acid,        glycodeoxycholic acid, glycyrrhizic acid, glycyrrhetinic acid        and salts thereof and at least one amphipathic substance        selected from the group consisting of a phosphatidylcholine        having 10 to 12 carbon atoms, a polyoxyethylene sorbitan        monofatty acid ester having 12 to 18 carbon atoms, a sorbitan        fatty acid ester having 16 to 18 carbon atoms, glycerol        monooleate, glycerol dilaurate, glycerol distearate, glycerol        dioleate, polyoxyethylene castor oil and α-tocopherol and which        is capable of developing a membrane disruptive function        promoting effect.    -   (2) The pH sensitive carrier set forth in (1) above, wherein the        pH sensitive compound and the amphipathic substance form        micellar particles.    -   (3) The pH sensitive carrier set forth in (2) above, wherein the        particle size is 10 to 200 nm.    -   (4) The pH sensitive carrier set forth in any one of (1) to (3)        above, wherein the pH sensitive compound is present in an amount        of not less than 10 moles per 100 moles of the amphipathic        substance.    -   (5) The pH sensitive carrier set forth in any one of (1) to (4)        above, wherein when a leakage of the pH sensitive compound alone        in a leaching test is taken as La, a leakage of the amphipathic        substance alone taken as Lb, a leakage of the pH sensitive        carrier taken as Lc, leakages at a pH of 7.4, respectively,        taken as Lc_(7.4)) La_(7.4) and Lb_(7.4), and leakages at a pH        of 5.0 or 4.5, respectively, taken as Lc_(x), La_(x) and Lb_(x),        Δ represented by the following equation (1) is not smaller than        5 and Δ′ represented by the following equation (2) is not        smaller than 5.

Δ=(Lc _(x) −Lc _(7.4))−(La _(x) −La _(7.4))  Equation (1)

Δ′=Lc _(x)−(La _(x) +Lb _(x))  Equation (2)

(6) A pH sensitive drug, wherein the pH sensitive carrier defined in anyone of (1) to (5) above supports a physiologically active substance.

(7) The pH sensitive drug set forth in (6) above, wherein thephysiologically active substance is made of a protein or a peptide.

(8) A pH sensitive drug composition including the pH sensitive carrierand the physiologically active substance, defined in any one of (1) to(5) above.

(9) The pH sensitive drug composition set forth in (8) above, whereinthe physiologically active substance is a protein or a peptide.

(10) A method for preparing a pH sensitive carrier which is capable ofdeveloping a membrane disruptive function promoting effect, the methodincluding associating at least one pH sensitive compound selected fromthe group consisting of deoxycholic acid, cholic acid, ursodeoxycholicacid, chenodeoxycholic acid, hyodeoxycholic acid, C27 bile acid,glycodesoxycholic acid, glycyrrhizic acid, glycyrrhetinic acid and saltsthereof and at least one amphipathic substance selected from the groupconsisting of a phosphatidylcholine having 10 to 12 carbon atoms, apolyoxyethylene sorbitan monofatty acid ester having 12 to 18 carbonatoms, a sorbitan fatty acid ester having 16 to 18 carbon atoms,glycerol monooleate, glycerol dilaurate, glycerol distearate, glyceroldioleate, polyoxyethylene castor oil and α-tocopherol.

(11) A method for treating or preventing a disease, the method includingcollecting cells from a subject, culturing the collected cells in amedium containing the pH sensitive drug set forth in (6) or (7) aboveand/or the pH sensitive drug composition set forth in (8) or (9) above,and administering the thus cultured cells to the subject.

In an illustrative embodiment, provided is a pH sensitive carrier whichincludes at least one pH sensitive compound selected from the groupconsisting of deoxycholic acid, cholic acid, ursodeoxycholic acid,chenodeoxycholic acid, hyodeoxycholic acid, C27 bile acid,glycodesoxycholic acid, glycyrrhizic acid, glycyrrhetinic acid and saltsthereof and at least one amphipathic substance selected from the groupconsisting of a phosphatidylcholine having 10 to 12 carbon atoms, apolyoxyethylene sorbitan monofatty acid ester having 12 to 18 carbonatoms, a sorbitan fatty acid ester having 16 to 18 carbon atoms,glycerol monooleate, glycerol dilaurate, glycerol distearate, glyceroldioleate, polyoxyethylene castor oil and α-tocopherol and is capable ofdeveloping a membrane disruptive function promoting effect. The pHsensitive carrier may be sometimes hereinafter referred to as “carrier,”“associated product” or “complex.” As used herein, the “number of carbonatoms” of the described amphipathic substance means the number of carbonatoms of a fatty acid moiety (acyl group) serving as the hydrophobicsite of the amphipathic substance.

In an illustrative embodiment, there can be provided a pH sensitivecarrier which is superior in safety and has superior pH sensitivity.

As used herein, the term “membrane disruptive function” means a functionof causing leakage in a leaching test. The leaching test used in thisspecification is one wherein liposomes (dispersion) including an aqueoussolution containing a quenching substance and a fluorescent substance,and a pH sensitive carrier or an evaluation sample dispersion such as ofa pH sensitive compound alone or an amphipathic compound alone is addedto an aqueous solution whose pH is adjusted to a given level, followedby incubating the aqueous solution at 37° C. for 90 minutes or 30minutes and measuring the fluorescence of the aqueous solution.According to this method, a fluorescent substance dissolved or leachedout from the liposomes can be measured, from which the liposome membranedisruptive function of the pH sensitive carrier can be confirmed. Itwill be noted that the leaching test will be described in more detail inexamples appearing hereinafter.

As used herein, the term “to develop a membrane disruptive functionpromoting effect” means to satisfy both of requirements (1) and (2): (1)in the leaching test, a leakage at a given pH that is lower than aphysiological pH increases compared to a leakage at the physiological pHand the increase is greater than the increase where the pH sensitivecompound alone is subjected to the test; and (2) in the leaching test ata given pH less than the physiological pH, a leakage at the time when apH sensitive compound and an amphipathic substance forms a complex (pHsensitive carrier) is greater than the sum of a leakage of the pHsensitive compound alone and a leakage of the amphipathic substancealone. More particularly, to develop a membrane disruptive functionpromoting effect means that in leaching tests at a pH of 7.4 and at a pHof 5.0 or 4.5, a leakage Lc of a pH sensitive carrier (a complex of a pHsensitive compound and an amphipathic substance) satisfies both thefollowing relations with a leakage La of the pH sensitive compound aloneand a leakage Lb of the amphipathic substance alone. More particularly,the above (1) is represented by the following formula (1) and the above(2) is represented by the following formula (2). It is to be noted thatin the following formulas, leakages at a pH of 7.4 are, respectively,denoted by Lc_(7.4), La_(7.4) and Lb_(7.4), and leakages at a pH of 5.0or 4.5 are, respectively, denoted by Lc_(x), La_(x) and Lb_(x).

Δ=(Lc _(x) −Lc _(7.4))−(La _(x) −La _(7.4))>0  Formula (1)

Δ′=Lc _(x)−(La _(x) +Lb _(x))>0  Formula (2)

In the above formula (1), Δ should exceed 0 and is typically not lessthan 5, for example not less than 10 and for example not less than 30.In the above formula (2), Δ′ typically exceeds 0, for example not lessthan 5, for example not less than 10, for example not less than 15.

An illustrative pH sensitive carrier is one whose Δ and Δ′ are,respectively, not less than 5 in the above formulas (1) and (2) andwhich contains a bile acid and a lipid. Another illustrative pHsensitive carrier is one whose Δ and Δ′ in the formulas (1) and (2) are,respectively, not less than 5 and which contains glycyrrhizic acid orglycyrrhetinic acid and a lipid.

As used herein, the term “physiological pH” means a pH in a normaltissue or normal body fluid. The physiological pH is generally at 7.4and may differ, more or less (±0.10), depending on the normal tissue ornormal body fluid. The term “a given pH less than a physiological pH”means a pH less than 7.4, for example a pH of not less than 3.0 to lessthan 7.4, for example a pH of not less than 4.0 to less than 7.3, forexample a pH of not less than 4.5 to less than 7.0.

Although how the pH sensitive carrier develops a membrane disruptivefunction promoting effect is not clear, this is assumed in the followingway. It will be noted that this theory should not be construed as anylimitation.

It is considered that the pH sensitive carrier is formed by associationof a pH sensitive compound and an amphipathic substance in an aqueoussolution at a pH level not lower than a physiological pH.

In FIG. 1A, a pH sensitive carrier and a pH sensitive drug wherein thepH sensitive carrier supports a physiologically active substancetherewith are schematically shown. As shown in FIG. 1A, it is consideredthat the pH sensitive carrier is formed by association of a pH sensitivecompound with an amphipathic substance at a hydrophobic site thereof.The pH sensitive carrier can include a physiologically active substancetherein. It will be noted that the form of the association of the pHsensitive carrier is based on assumption and thus, the pH sensitivecarrier is not limited to this form of association. The form of supportof the pH sensitive carrier is based on assumption and thus, the pHsensitive carrier should not be construed as limited to this form ofsupport.

It is considered that the pH sensitive carrier has a membrane disruptivefunction promoting effect as a result that if an ambient environmentbecomes a pH lower than a physiological pH, the pH sensitive carrierchanges in association form between the pH sensitive compound and theamphipathic substance. For instance, it is assumed that if the pHbecomes lower than a physiological pH in a system where a pH sensitivecarrier and a biological membrane (e.g., a cell membrane, a vesicularmembrane or the like) exist, the association form of the pH sensitivecarrier changes. After contact with the biological membrane, thestructural change of the biological membrane is caused by the change ofthe association form. More particularly, the pH sensitive carrier causesthe structural change of the biological membrane. This is considered asfollows: when the pH changes to weak acidity, the pH sensitive compoundin the pH sensitive carrier becomes unstable in the structure of thecarrier, with the result that the pH sensitive carrier is rearrangedwith the biological membrane existing in the system, thereby developingthe membrane disruptive function promoting effect. In other words, it isconsidered that the pH sensitive compound is a molecule that acts tochange the solubility toward the hydrophobic association throughprotonation when the pH becomes weakly acidic. More particularly, thehydrophobic association involving the pH sensitive compound is inresponse to a weakly acidic environment and is able to develop thefunction. As used herein, the term “membrane disruption” refers to achange in such a membrane structure and may not always involveseparation or decomposition of all of the membrane constituentcomponents. Owing to the occurrence of such “membrane disruption, thecomponents contained inside the biological membrane (e.g., endosome)leach to outside of the biological membrane.

The pH sensitive carrier typically is one whose leakage, determined bythe leaching test, is less than 20% at a pH of 7.4 and is larger than20% at a pH of 4.0. For example, the leakage in the leaching test isless than 20% at a pH of 6.5 and larger than 20% at a pH of 4.0.Moreover, the leakage at a pH of 7.4 or 6.5 can be not larger than 15%,for example not larger than 10%. The leakage at a pH of 4.0 is typicallynot less than 40%, for example not less than 50%. When the leakage ofthe pH sensitive carrier is set as defined above, the development of themembrane disruptive function promoting effect at a weakly acidic pH canbe better shown.

The pH sensitive carrier is also able to develop a membrane fusionfunction promoting effect along with the membrane disruptive functionpromoting effect.

As used herein, the term “membrane fusion function” means a function ofcausing membrane fusion in a membrane fusion test. The membrane fusiontest used herein is a test wherein a liposome (dispersion) incorporatingtwo types of fluorescent substances in a bimolecular membrane, and a pHsensitive carrier or an evaluation sample dispersion such as of a pHsensitive compound alone, an amphipathic substance alone or the like areadded to an aqueous solution adjusted to a given pH, and the resultingaqueous solution is incubated at 37° C. for 60 minutes, followed bymeasurement of the fluorescence of the aqueous solution. According tothis method, variations in energy resonance transfer of the two types offluorescent substances incorporated in the liposome can be measured,thus confirming the membrane fusion function of the pH sensitivecarrier. It is to be noted that the membrane fusion test is described indetail in examples appearing hereinafter.

As used herein, the term “to develop a membrane fusion functionpromoting effect” means that, in the membrane fusion test, a fusion rateat a given pH less than a physiological pH increases compared to afusion rate at the physiological pH and the increase is larger thancompared to where a pH sensitive compound alone is used for the test.More particularly, to develop the membrane fusion function promotingeffect means that in the membrane fusion tests at pHs of 7.4 and 5.0, afusion rate Rc (%) of a pH sensitive carrier (a complex of a pHsensitive compound and an amphipathic substance) and a fusion rate Ra(%) of the pH sensitive compound alone satisfy the relationship of thefollowing Formula (3). It will be noted that the fusion rates at a pH of7.4 are, respectively, represented by Rc_(7.4) and Ra_(7.4) and thefusion rates at a pH of 5.0 are, respectively, represented by Rc_(x) andRa_(y).

ΔR=(Rc _(x) −Rc _(7.4))−(Ra _(x) −Ra _(7.4))>0  Formula (3)

In the formula (3), ΔR should exceed 0, for example not less than 2, forexample not less than 5, for example not less than 10.

An illustrative pH sensitive carrier is one whose ΔR in the aboveformula (3) is not less than 2 and which contains a bile acid and alipid.

The pH sensitive carrier develops the membrane fusion function promotingeffect at a weakly acidic pH (at a given pH lower than a physiologicalpH). Although this mechanism is not fully understood, it is assumed thatsuch a mechanism as set out with respect to the membrane disruptivefunction promoting effect is applied. It will be noted that thisassumption should not be construed as a limitation.

In particular, it is assumed that the pH sensitive carrier changes inassociation form between the pH sensitive compound and the amphipathicsubstance if an ambient environment becomes less than the physiologicalpH, so that membrane fusion occurs due to the rearrangement with abiological membrane existing in the system. On this occasion, therearrangement ascribed to the fusion occurs among affinity componentsthemselves with no affinity for biological membrane, or low affinitycomponents (e.g., a physiologically active substance) are excluded orreleased from the rearranged membrane.

Generally, an extracellular molecule is surrounded by an endosome thatis a sort of biological membrane and taken up in a cell. Thereafter, thepH inside the endosome is lowered by the action of a proton pump.Moreover, the endosome fuses with a lysosome containing a hydrolase, sothat the extracellular molecule is decomposed. Hence, most of theextracellular molecules are not delivered to within the cellularcytosol.

In contrast thereto, the pH sensitive carrier (pH sensitive drug or pHsensitive drug composition) is surrounded by an endosome and taken up ina cell as shown in FIGS. 1B and 1C, thereby leading likewise to anenvironment where the pH is lower. In association with the lowering(acidification) of pH, the pH sensitive compound causes the pH sensitivecarrier to be instabilized, so that membrane rearrangement between theendosome and the pH sensitive carrier occurs thereby causing themembrane disruptive function (sometimes, the membrane disruptivefunction occurring along with the membrane fusion function in somecases) caused by the pH sensitive carrier.

As exemplified in FIGS. 1B and 1C, the use of the pH sensitive carrierpermits a physiologically active substance and the like to be deliveredinto the cellular cytosol. More particularly, when a pH sensitive drugis used, a physiologically active substance (FIG. 1B) included in the pHsensitive carrier, or a physiologically active substance (FIG. 1C) usedalong with the pH sensitive carrier with the case of using a pHsensitive drug composition is surrounded with an endosome along with thepH sensitive carrier and taken up in the endosome. When the pH insidethe endosome is lowered, the pH sensitive compound causes the pHsensitive carrier to be unstable thereby causing the membranerearrangement between the endosome and the pH sensitive carrier. As aconsequence, the membrane disruption of the endosome with the pHsensitive carrier takes place. In this way, the physiologically activesubstance is released to the cellular cytosol. That is, delivery intothe cellular cytosol can be realized without involving decomposition ofthe physiologically active substance.

An illustrative pH sensitive carrier can form a complex containing a pHsensitive compound and an amphipathic substance in an aqueous medium.The form of the complex is not critical, and the pH sensitive compoundand the amphipathic substance may form a membrane or part or all of thepH sensitive compound may be embedded in the structure formed of theamphipathic substance through association. In the illustrative pHsensitive carrier, the pH sensitive compound and the amphipathicsubstance can form micellar particles, or a particulate carrier such asof liposome may be formed. Where the EPR (Enhanced Permeation andRetention) effect and endocytosis are taken into consideration, themicellar particles typically have a size of 10 to 200 nm. For example,the size is 10 to 100 nm. It will be noted that the micellar particleused herein means a particle formed as a result of a particulateassociation between the pH sensitive compound and the amphipathicsubstance by the hydrophobic interaction. Typically, particles of amonomolecular membrane structure are mentioned, but not including thoseforming a bimolecular lipid membrane structure (e.g., liposome). Theparticle size of the pH sensitive carrier indicated in thisspecification can be measured according to a dynamic light scatteringmethod (Nano ZS 90, made by MALVERN Instruments Ltd).

It should be noted that it is sufficient that a pH sensitive carrierexists in an aqueous solution containing the pH sensitive carrier evenif a pH sensitive compound or an amphipathic substance exists in freestate without forming an associate.

The respective components of the pH sensitive carrier are now described.

Constituent components of pH sensitive carrier

(pH Sensitive Compound)

As a pH sensitive, mention is made of at least one selected from thegroup consisting of deoxycholic acid, cholic acid, ursodeoxycholic acid,chenodeoxycholic acid, hyodeoxycholic acid, C27 bile acid,glycodeoxycholic acid, glycyrrhizic acid, glycyrrhetinic acid and saltsthereof. The salts of the pH sensitive compound are not critical, forwhich mention is made of salts of alkali metals such as lithium, sodium,potassium and the like, salts of alkaline earth metals such asmagnesium, calcium, barium and the like, and ammonium salts. These pHsensitive compounds may be used singly or in combination of two or more.

Illustrative pH sensitive compounds include deoxycholic acid,ursodeoxycholic acid, chenodeoxycholic acid, hyodeoxycholic acid,glycodesoxycholic acid, glycyrrhizic acid or salts thereof, of whichdeoxycholic acid, ursodeoxycholic acid, glycyrrhizic acid or saltsthereof are specific examples.

Deoxycholic acid, cholic acid, ursodeoxycholic acid, chenodeoxycholicacid, hyodeoxycholic acid, C27 bile acid and glycodesoxycholic acid,which are illustrative examples, are generically called “bile acid”. Thebile acid has been known as a typical steroid derivative since beforethe 1920s and has been utilized in the field of bacteriology. The bileacid forms complexes with cholesterol, lipids and fat-soluble vitaminsin the human body and has a role of supplementing absorption thereof.Moreover, because of the capability of forming complexes with lipids,proteins and hydrophobic materials in view of physicochemical propertiesof the bile acid, it has been long utilized for isolation andpurification of proteins and also as a solubilizer or emulsifier. Inrecent years, attention has been paid to the use in a preparationprocess of vaccine and also to as an absorption enhancer for drugthrough a bile acid transporter. Sodium deoxycholate (also known assodium desoxycholate) and ursodeoxycholic acid (also known asursodesoxycholic acid) have been approved as a pharmaceutical additivecapable of being injected to humans, respectively, and their superiorsafety performance has been recognized. Accordingly, deoxycholic acid,ursodeoxycholic acid or salts thereof (e.g., sodium salts) can be usedas the pH sensitive compound.

The pH sensitive compound is typically present in an amount of not lessthan 10 moles per 100 moles of amphipathic substance. For example, it ispresent in an amount 10 to 640 moles, for example at 20 to 320 moles,for example at 20 to 160 moles per 100 moles of amphipathic substance.

Amphipathic Substance

The amphipathic substance includes at least one selected from the groupconsisting of a phosphatidylcholine having 10 to 12 carbon atoms, apolyoxyethylene sorbitan monofatty acid ester having 12 to 18 carbonatoms, a sorbitan fatty acid ester having 16 to 18 carbon atoms,glycerol monooleate, glycerol dilaurate, glycerol distearate, glyceroldioleate, polyoxyethylene castor oil and α-tocopherol. These amphipathicsubstances may be used singly or in combination of two or more. As usedherein, the “number of carbon atoms” of amphipathic substance in thepresent specification means the number of carbon atoms of a fatty acidmoiety (acyl group) serving as the hydrophobic site of the amphipathicsubstance.

As a phosphatidylcholine having 10 to 12 carbon atoms, adiacylphosphatidylcholine having a saturated acyl group can be used, forwhich mention is made, for example, of didecanoylphosphatidylcholine(DDPC: 1,2-didecanoyl-sn-glycero-3-phosphatidylcholine) anddilauroylphosphatidylchlorine (DLPC:1,2-dilauroyl-sn-glycero-3-phosphatidylcholine). The phophatidylcholinemay be either a naturally-derived one or a synthesized one obtained byknown processes, or commercially available ones may also be used.

For a polyoxyethylene sorbitan monofatty acid ester having 12 to 18carbon atoms, mention is made of a polyoxyethylene sorbitan monolauricacid ester (polyoxyethylene sorbitan monolaurate), polyoxyethylenesorbitan myristic acid ester (polyoxyethylene sorbitan monomyristate),polyoxyethylene sorbitan monopalmitic acid ester (polyoxyethylenesorbitan palmitate), polyoxyethylene sorbitan monostearic acid ester(polyoxyethylene sorbitan monostearate), polyoxyethylene sorbitanmonooleic acid ester (polyoxyethylene sorbitan monooleate) and the like.Although the degree of polymerization of the polyoxyethylene is notcritical, the degree of polymerization with respect to the total ofpolyethylene chains added to the sorbitan can be 10 to 200, for example15 to 100, for example 20 to 50. The polyoxyethylene sorbitan monofattyacid ester may be either a synthetized one or a commercial product.Commercial products of the polyoxyethylene sorbitan monofatty acid estercan include, for example, those commercially sold under the designationsof Tween 20 (polyoxyethylene sorbitan monolauric acid ester), Tween 40(polyoxyethylene sorbitan monopalmitic acid ester), Tween 60(polyoxyethylene sorbitan monostearic acid ester) and Tween 80(polyoxyethylene sorbitan monooleic acid ester). Of these,polyoxyethylene sorbitan monofatty acid esters (Tween 40, Tween 60 andTween 80) having 16 to 18 carbon atoms are specific examples.

As a sorbitan fatty acid ester having 16 to 18 carbon atoms, mention ismade of sorbitan monofatty acid esters such as sorbitan monopalmiticacid ester (sorbitan monopalmitate), sorbitan monostearic acid ester(sorbitan monostearate), sorbitan monooleic acid ester (sorbitanmonooleate) and the like, and sorbitan trifatty acid esters such assorbitan tripalmitic acid ester (sorbitan tripalmitate), sorbitantristearic acid ester (sorbitan tristearate), sorbitan trioleic acidester (sorbitan trioleate) and the like. The sorbitan fatty acid esterused may be either a synthesized one or a commercial product. As acommercial product of the sorbitan fatty acid ester, there can be used,for example, those sold under the designations of SPAN 40 (sorbitanpalmitic acid ester), SPAN 60 (sorbitan stearic acid ester), SPAN 80(sorbitan oleic acid ester), SPAN 65 (sorbitan tristearic acid ester),and SPAN 85 (sorbitan trioleic acid ester). Of these, SPAN 80, SPAN 65and SPA 85 are particular examples.

Glycerol monooleate (glyceryl monooleate), glycerol dilaurate (glyceryldilaurate), glycerol distearate (glyceryl distearate) and glyceroldioleate (glyceryl dioleate) are acyl glycerols wherein one or twomolecules of a fatty acid are ester-bound to glycerol provided that thesites at which the fatty acid is bound are not critical. For instance,with glycerol monooleate that is a monoacyl glycerol, the fatty acid maybe bound to at the C1 position or C2 position of glycerin. With glyceroldilaurate, glycerol distearate and glycerol dioleate which are each adiacyl glycerol, the fatty acid may be ester bound to at the C1 and C2positions or at the C1 and C3 positions of glycerin. As a glyceroldilaurate, for example, α,α′-dilaurate which is substituted at the C1and C3 positions can be used. As glycerol distearate or glyceroldioleate, a diacyl glycerol which is substituted at the C1 and C2positions can be used. These glycerol derivatives may be synthesizedones or commercial products, respectively.

As a polyoxyethylene castor oil, mention is made of adducts ofpolyoxyethylenes to castor oil. The degree of polymerization ofpolyoxyethylene is not critical and can be 3 to 200, for example 5 to100, for example 10 to 50. The polyoxyethylene castor oil may be asynthesized one or a commercial product.

For α-tocopherol, there may be used either naturally derived ones orones prepared by known processes, and commercial products may also beused.

As these amphipathic substances, phosphatidylcholines having 10 to 12carbon atoms can be used, of which dilauroylphosphatidylcholine (DLPC)having 12 carbon atoms are particular examples.

Combinations of the pH sensitive compound and the amphipathic substancecan also be used.

The pH sensitive carrier is able to develop a membrane disruptivefunction promoting effect at a desired pH by the proper combination of apH sensitive compound and an amphipathic substance. On this occasion,the pH at which the pH sensitive carrier commences to develop themembrane disruptive promoting effect differs depending on thecombination of a pH sensitive compound and an amphipathic substance.This is considered for the following reasons: pKa differs depending onthe type of pH sensitive compound and the manner of forming associationwith an amphipathic substance also differs depending on the combinationof a pH sensitive compound and an amphipathic substance. Accordingly,when a combination of a pH sensitive compound and an amphipathicsubstance is appropriately changed, the proper choice of the pH at whichthe function can be developed is possible, thus enabling in vivodelivery and intracellular delivery to be designed in detail.

In the pH sensitive carrier, illustrative combinations of pH sensitivecompounds and amphipathic substances include deoxycholic acid and DDPC,deoxycholic acid and DLPC, deoxycholic acid and Tween 20, deoxycholicacid and Tween 40, deoxycholic acid and Tween 60, deoxycholic acid andTween 80, deoxycholic acid and SPAN 40, deoxycholic acid and SPAN 60,deoxycholic acid and SPAN 80, deoxycholic acid and SPAN 65, deoxycholicacid and SPAN 85, deoxycholic acid and α-tocopherol, deoxycholic acidand glycerol monooleate, deoxycholic acid and glycerol distearate,deoxycholic acid and glycerol dioleate, deoxycholic acid and glyceroldilaurate (α,α′-dilaurin), deoxycholic acid and polyoxyethylene castoroil, ursodeoxycholic acid and DDPC, ursodeoxycholic acid and DLPC,ursodeoxycholic acid and Tween 20, ursodeoxycholic acid and Tween 40,ursodeoxycholic acid and Tween 60, ursodeoxycholic acid and Tween 80,ursodeoxycholic acid and SPAN 40, ursodeoxycholic acid and SPAN 60,ursodeoxycholic acid and SPAN 80, ursodeoxycholic acid and SPAN 65,ursodeoxycholic acid and SPAN 85, ursodeoxycholic acid and α-tocopherol,ursodeoxycholic acid and glycerol monooleate, ursodeoxycholic acid andglycerol distearate, ursodeoxycholic acid and glycerol dioleate,ursodeoxycholic acid and glycerol dilaurate (α,α′-dilaurin),ursodeoxycholic acid and polyoxyethylene castor oil, glycyrrhizic acidand DDPC, glycyrrhizic acid and DLPC, glycyrrhizic acid and Tween 20,glycyrrhizic acid and Tween 40, glycyrrhizic acid and Tween 60,glycyrrhizic acid and Tween 80, glycyrrhizic acid and SPAN 40,glycyrrhizic acid and SPAN 60, glycyrrhizic acid and SPAN 80,glycyrrhizic acid and SPAN 65, glycyrrhizic acid and SPAN 85,glycyrrhizic acid and α-tocopherol, glycyrrhizic acid and glycerolmonooleate, glycyrrhizic acid and glycerol distearate, glycyrrhizic acidand glycerol dioleate, glycyrrhizic acid and glycerol dilaurate(α,α′-dilaurin), and glycyrrhizic acid and polyoxyethylene castor oil.

More specifically, mention is made of deoxycholic acid and DDPC,deoxycholic acid and DLPC, deoxycholic acid and Tween 40, deoxycholicacid and Tween 60, deoxycholic acid and Tween 80, deoxycholic acid andSPAN 40, deoxycholic acid and SPAN 65, deoxycholic acid and SPAN 85,deoxycholic acid and α-tocopherol, deoxycholic acid and monoolein,deoxycholic acid and polyoxyethylene castor oil, ursodeoxycholic acidand DDPC, ursodeoxycholic acid and DLPC, ursodeoxycholic acid and Tween40, ursodeoxycholic acid and Tween 60, ursodeoxycholic acid and Tween80, ursodeoxycholic acid and SPAN 40, ursodeoxycholic acid and SPAN 65,ursodeoxycholic acid and SPAN 85, ursodeoxycholic acid and α-tocopherol,ursodeoxycholic acid and monoolein, ursodeoxycholic acid andpolyoxyethylene castor oil, glycyrrhizic acid and DDPC, glycyrrhizicacid and DLPC, glycyrrhizic acid and Tween 40, glycyrrhizic acid andTween 60, glycyrrhizic acid and Tween 80, glycyrrhizic acid and SPAN 40,glycyrrhizic acid and SPAN 65, glycyrrhizic acid and SPAN 85,glycyrrhizic acid and α-tocopherol, glycyrrhizic acid and monoolein, andglycyrrhizic acid and polyoxyethylene castor oil.

Aqueous Solvent

The pH sensitive carrier may be contained in an aqueous solution. Itwill be noted that an aqueous solution containing a pH sensitive carriermay also be hereinafter referred to as “carrier dispersion.”

As a solvent of the aqueous solution containing a pH sensitive carrier,there is mentioned an aqueous solution containing a buffer, NaCl or asugar such as glucose, sucrose or the like.

For the buffer, known buffers can be conveniently used so far as theyare able to maintain the pH of an aqueous solution containing a pHsensitive carrier at a level no less than a physiological pH and nospecific limitation is placed thereon. The buffers include, for example,a phosphate buffer, a citrate buffer, a citrate-phosphate buffer, atrishydroxymethylaminomethane-HCl buffer (Tris hydrochloride buffer),Good's buffers such as an MES buffer (2-morpholinoethanesulfonatebuffer), a TES buffer(N-tris(hydroxymethyl)methyl-2-aminoethanesulfonate buffer), an acetatebuffer, an MOPS buffer (3-morpholinopropanesulfonate buffer), anMOPS—NaOH buffer, an HEPES buffer(4-(2-hydroxyethyl)-1-piperazineethanesulfonate buffer), an HEPES—NaOHbuffer and the like, amino acid buffers such as a glycine-hydrochloridebuffer, a glycine-NaOH buffer, a glycylglcyine-NaOH buffer, aglycylglycine-KOH buffer and the like, boron buffers such as aTris-borate buffer, a borate-NaOH buffer and a borate buffer, or animidazole buffer. Of these, a phosphate buffer, a citrate buffer, acitrate-phosphate buffer, a Tris-hydrochloride buffer, an MES buffer, anacetate buffer and an HEPES—NaOH buffer are particular examples. Theconcentration of a buffer is not critical and can be 0.1 to 200 mM, forexample 1 to 100 mM. It will be noted that the concentration of a buffermeans a concentration (mM) of a buffer contained in an aqueous solution.

The concentration of NaCl or a sugar such as glucose, sucrose or thelike is not critical and is typically 0.1 to 200 mM, for example 1 to150 mM.

The concentration of the pH sensitive carrier in an aqueous solution isnot critical and is such that a total molar concentration of a pHsensitive compound and an amphipathic substance is typically 0.73μmols/liter to 7.4 mmols/liter, for example 7.3 mmols/liter to 6.5mmols/liter, for example 8.0 μmols/liter to 4.2 mmols/liter.

Other Components

The pH sensitive carrier may further contain other components, such as astabilizer, in the pH sensitive carrier or aqueous solution containingthe pH sensitive carrier. The content of these components is notcritical unless the pH sensitive carrier is destroyed and is typicallynot larger than 150 mols, for example not larger than 66.4 mols per 100mols of the amphipathic substance.

The stabilizer is not critical in type unless the pH sensitive carrieris destroyed and known stabilizers are usable including, for example:saturated or unsaturated alcohols having 4 to 20 carbon atoms such as1-octanol, 1-dodecanol, 1-hexadodecanol, 1-eicosanol and the like;saturated or unsaturated fatty acids having 12 to 18 carbon atoms suchas lauric acid, myristic acid, palmitic acid, stearic acid, oleic acidand the like; alkyl (alkyl having 1 to 3 carbon atoms) esters ofsaturated or unsaturated fatty acids having 8 to 18 carbon atoms such asmethyl caprylate (methyl octanoate), methyl caprylate (ethyl octanoate),methyl laurate, ethyl laurate, ethyl myristate, ethyl palmitate, ethylstearate, methyl oleate, ethyl oleate and the like; D(L)-amino acidssuch as D(L)-alanine, alginin, asparagine, aspartic acid, cysteine,glutamine, glycine, histidine, leucine, isoleucine, lysine, methionine,proline, serine, threonine, tryptophan, tyrosine, valin, phenylalanineand the like; amino acid triglycerides such as tricaproin, tricaprylinand the like; polyoxyethylene sorbitan trifatty acid esters having 12 to18 carbon atoms (e.g., Tween 65, Tween 85) such as polyoxyethylenesorbitan tripalmitic acid ester, polyoxyethylene sorbitan trioleic acidester and the like; polyoxyethylene alkyl esters having 12 to 18 carbonatoms (e.g., PEG-20 stearyl ether, PEG-23 lauryl ether) such aspolyoxyethylene lauric acid ester, polyoxyethylene myristic acid ester,polyoxyethylene palmitic acid ester, polyoxyethylene stearic acid esterand the like; polyoxyalkylene hardened castor oils (e.g., PEG-10hardened castor oil, PEG-40 hardened castor oil and PEG-60 hardenedcastor oil); glycerol esters of saturated or unsaturated monofatty acidshaving 8 to 18 carbon atoms such as caprylin (glycerol octenoate),glycerol monocaprylate, glycerol monolaurate, glycerol monomyristate,glycerol monopalmitate, glycerol monostearate, glycerol monooleate andthe like; glycerol esters of difatty acids having 8 to 16 carbon atomssuch as glycerol dioctanoate, glycerol dicaprylate, glycerol dilaurate,glycerol dimyristate, glycerol dipalmitate and the like; andα-tocopherol acetic ester, castor oil, soybean oil, cholesterol,squalene, squalane, lactose, ascorbyl palmitate, benzyl benzoate, methylparaoxybenzoate, ethyl paraoxybenzoate, propyl paraoxybenzoate, butylparaoxybenzoate and the like. As used herein, the “number of carbonatoms” means the number of carbon atoms of a fatty acid moiety (acylgroup) serving as the hydrophobic site.

Method of Preparing a pH Sensitive Carrier

In a further illustrative aspect, there is provided a method forpreparing a pH sensitive carrier capable of developing a membranedisruptive function promoting effect, which method including associatingat least one pH sensitive compound selected from the group consisting ofdeoxycholic acid, cholic acid, ursodeoxycholic acid, chenodeoxycholicacid, hyodeoxycholic acid, C27 bile acid, glycodesoxycholic acid,glycyrrhizic acid, glycyrrhetinic acid and salts thereof and at leastone amphipathic substance selected from the group consisting of aphosphatidylcholine having 10 to 12 carbon atoms, a polyoxyethylenesorbitan monofatty acid ester having 12 to 18 carbon atoms, a sorbitanfatty acid ester having 16 to 18 carbon atoms, glycerol monooleate,glycerol dilaurate, glycerol distearate, glycerol dioleate,polyoxyethylene castor oil and α-tocopherol.

For the association of the pH sensitive compound and the amphipathicsubstance, it is sufficient to bring the pH sensitive compound and theamphipathic substance into contact with each other in an aqueoussolution. Thus, the pH sensitive carrier can be prepared by bringing thepH sensitive compound and the amphipathic substance into mutual contactin an aqueous solution. For example, an aqueous solution containing a pHsensitive compound and an amphipathic substance is prepared and issubsequently subjected to dispersion under vigorous agitation by use ofan emulsifying machine, a vortex mixer, ultrasonic waves or the like, bywhich there can be obtained a pH sensitive carrier in the form of the pHsensitive compound and the amphipathic substance being associated.

For the preparation of an aqueous solution containing a pH sensitivecompound and an amphipathic substance, no specific limitation is placedthereon so far as an associated product of the pH sensitive compound andthe amphipathic substance is formed. For instance, mention is made of:(1) a method wherein an aqueous solution containing a pH sensitivecompound and an aqueous solution containing an amphipathic substance areseparately prepared, and these aqueous solutions are mixed, followed bydispersion under vigorous agitation by use of an emulsifying machine, avortex mixer, ultrasonic waves or the like to obtain a pH sensitivecarrier; and (2) a preparation method using the Bangham method known asa method of preparing a liposome. More specifically, according to theBangham method, constituent components of the pH sensitive carrier suchas a pH sensitive compound and an amphipathic substance are dissolved inan organic solvent (e.g., methanol or chloroform) in a glass containerand the organic solvent is removed such as with a rotary evaporator toform a thin film on the walls of the glass container. Next, an aqueoussolution is added to the glass container formed with the thin film,followed by swelling the thin film at a normal a temperature (5 to 35°C.) and shaking the glass container at a normal temperature (5 to 35°C.). On this occasion, while vigorously agitating by means of anemulsifying machine, a vortex mixer or ultrasonic waves, the thin filmcan be well dispersed in the aqueous solution. In the above preparationmethod (1), a pH sensitive compound may be mixed in an aqueous solutioncontaining an amphipathic substance. It will be noted that a solvent forthe aqueous solution may be such a solvent as used for the aqueoussolution set out hereinbefore.

It will also be noted that as to the details of the Bangham method,reference can be made to known methods of preparing liposomes asdescribed in “Liposomes” (edited by Shoushichi Nojima, Jyunzou Sunamotoand Keizou Inoue, and published by Nankoudou) and “Liposomes in LifeScience” (edited by Hiroshi Terada and Tetsuro Yoshimura, and publishedby Springer-Verlag, Tokyo).

The manner of adding other components such as a stabilizer, which may becontained in a pH sensitive carrier or in an aqueous solution containingthe pH sensitive carrier, is not critically limited. For instance, thecomponents may be added to an aqueous solution containing a pH sensitivecompound or an aqueous solution containing an amphipathic substance.Alternatively, when preparing a thin film, the components may bedissolved along with the constituent components of the pH sensitivecarrier, after which using the resulting thin film containing thesecomponents, there can be obtained an aqueous solution containing a pHsensitive carrier.

The pH sensitive carrier obtained in a manner as stated above is able todevelop such a membrane disruptive function promoting effect and can beconveniently used for DDS.

<pH Sensitive Drug and pH Sensitive Drug Composition>

According to an illustrative embodiment, there is provided a pHsensitive drug wherein a pH sensitive carrier supports at least onephysiologically active substance therewith.

As used herein, the term “support” means a form of a physiologicallyactive substance included in a carrier, a form of the substance insertedinto the carrier, or a form of the substance bound directly or via amedium to the surface of the carrier. As used herein, the term “bound”means either chemically bound with covalent bond or ionic bond orphysically bound with van der Waals bond or hydrophobic bond. Thephysiologically active substance may be either a hydrophilic substanceor hydrophobic substance. If the physiologically active substance ismade of a hydrophobic substance, the active substance is typicallysupported in the form of being included in a pH sensitive carrier orbeing inserted into the pH sensitive carrier. Where the physiologicallyactive substance is hydrophilic in nature, the substance can besupported in the form of being bound directly or via a medium to thecarrier surface.

The pH sensitive carrier is able to support a physiologically activesubstance. When the pH sensitive carrier develops the membranedisruptive function promoting effect in an environment of less than aphysiological pH, the supported physiologically active substance can bedelivered to a desired site. Although not clearly known, the mechanismfor this is assumed in the following way (see FIG. 1B). It will be notedthat no limitation should be based on the following assumption.

The pH sensitive drug wherein the pH sensitive carrier supports aphysiologically active substance is taken up in cells via endocytosisthereby forming an endosome containing the pH sensitive drug.Thereafter, the interior of the endosome leads to an acidic environment.On this occasion, when the ambient environment of the pH sensitive drugarrives at less than a physiological pH (e.g., a pH of 6.5), themembrane disruptive function promoting effect of the pH sensitivecarrier develops. More particularly, the constituent components of thepH sensitive carrier and the membrane components of the endosome arecaused to be rearranged, so that the physiologically active substancesupported with the pH sensitive carrier existing in the endosomemigrates to the cellular cytosol. This enables the physiologicalsubstance to be directly delivered to a desired cellular cytosol andthus, it is considered that such a high pharmacological effect is shown.

According to another illustrative embodiment, there is also provided apH sensitive drug composition including a pH sensitive carrier and atleast one physiologically active substance. On this occasion, thephysiologically active substance is present on outside (separately) ofthe pH sensitive carrier unlike the pH sensitive drug according to theabove embodiment, and the physiologically active substance and the pHsensitive carrier are not bound directly or via a medium. Moreparticularly, the pH sensitive drug composition according to thisembodiment is formed of a pH sensitive carrier and a physiologicallyactive substance being, respectively, mixed independently.

The pH sensitive drug composition wherein a pH sensitive carrier and aphysiologically active substance are respectively mixed independentlycan deliver the physiologically active substance to a desired site afterthe pH sensitive carrier develops the membrane disruptive functionpromoting effect in an environment whose pH is less than a physiologicalpH. Although not clearly known, the development mechanism is assumed tobe similar to the case of the pH sensitive drug wherein the pH sensitivecarrier supports a physiologically active substance (see FIG. 1C). It isnoted that no limitation should be based on the following assumption.

More particularly, the pH sensitive drug composition according to thisillustrative embodiment is taken up in the cell by the endocytosis ofthe pH sensitive carrier by the cell. At this time, along with the pHsensitive carrier, a physiologically active substance is also taken upin the cell by the endocytosis of the pH sensitive carrier by the cell.As a consequence, endosomes independently containing the pH sensitivecarrier and the physiologically active substance therein, respectivelyare formed. Thereafter, the inside of the endosomes is led to an acidicenvironment and the ambient environment arrives at less than aphysiological pH (e.g., a pH of 6.5), whereupon the membrane disruptivefunction promoting effect of the pH sensitive carrier develops. In doingso, the physiologically active substance existing in the inside of theendosomes migrates to the cellular cytosol. In this way, thephysiologically active substance can be delivered directly to a desiredcellular cytosol.

The pH sensitive drug and pH sensitive drug composition is able toefficiently deliver a physiologically active substance to a site ofliving body whose pH becomes lowered due to tumor or inflammation. Moreparticularly, the pH sensitive drug and pH sensitive drug compositioncan develop a membrane disruptive function promoting effect at a sitewhere the pH becomes lower, so that the physiologically active substancecan be selectively delivered to a treatment area such as ofinflammation.

The type of physiologically active substance to be supported with the pHsensitive carrier used in the pH sensitive drug and pH sensitive drugcomposition is not critical in type. For instance, as a physiologicallyactive substance, mention is made of a nucleic acid, a low molecularweight compound, a protein, and a peptide.

The nucleic acid includes one having a treating effect, such as siRNA,ODN (oligodeoxynucleotide), DNA or the like.

As a low molecular weight compound, mention is made of: antineoplasticssuch as mitomycin, docetaxel, methotrexate and the like; prodrugs suchas 5-aminolevulinic acid, protoporphyrin IX and the like;anti-inflammatory agents such as ganciclovir, dexamethasone, ribavirin,vidarabine and the like; contrast agents such asDOTA(1,4,7,10-tetraazacyclotetradecane-N,N′,N″,N″′-tetraacetic acid),DTPA(1,4,7,10-tetraazacyclodecane-N,N′,N″,N″′-tetraacetic acid) and thelike; and neuroprotectants such as edaravone and the like.

As a protein, mention is made of oxidoreductases such as SOD (superoxidedismutase), indophenoloxidase and the like; cytokines such as IL-10 andthe like, growth factors such as b-FGF and the like, thrombolytic agentssuch as t-PA and the like, hormones such as erythropoietin and the like,and anti-cell proteins PSD (Postsynaptic density protein), FNK (Anticelldeath factor) and the like; and antibodies such as Fab (Fragment), IgG,IgE and the like.

As a peptide, mention is made of: peptide drugs such as cyclosporin A,JIP-1 (JNK-interracting protein 1) and the like.

Variations of the described embodiments are understood by those ofordinary skill in the relevant art.

The amount of the physiologically active substance is not critical andcan be appropriately selected depending on the type of physiologicallyactive substance.

For the method of supporting a physiologically active substance in thepH sensitive carrier, there can be used any of known methods dependingon the type of physiologically active substance. Such methods are notcritical. For a method of obtaining a form of inclusion in the carrierand a form of insertion into the carrier, mention is made of a methodwherein after formation of a pH sensitive carrier according to theafore-stated method of preparing a pH sensitive carrier, the pHsensitive carrier is immersed in a solution containing a physiologicallyactive substance to permit the physiologically active substance to betaken in the pH sensitive carrier and a method wherein a solutioncontaining a physiologically active substance is charged into acontainer formed with a thin film according to the afore-stated methodof preparing a pH sensitive carrier thereby causing the physiologicallyactive substance to be included in the carrier. For a method ofobtaining a form of binding directly or via a medium to the surface ofthe carrier, mention is made of a method wherein a pH sensitive compoundor an amphipathic substance used as a constituent component of the pHsensitive carrier is introduced with a functional group capable ofreaction with a desired type of physiologically active substance and issubsequently reacted with the physiologically active substance to obtaina pH sensitive carrier bound with the physiologically active substance.It will be noted that the binding with the physiologically activesubstance may be made either prior to the preparation of the pHsensitive carrier or after the preparation.

The pH sensitive carrier and the physiologically active substance can bemixed according to any of known methods determined depending on the typeof physiologically active substance. Such methods are not critical, forwhich mention is made, for example, of a method wherein the carrier anda physiologically active substance are mixed with a medium such as anaqueous solvent, a diluent and the like.

The pH sensitive drug and the pH sensitive drug composition may furtherinclude other types of drug additives. Although the pH sensitive drugand pH sensitive drug composition may be in the form of solidpreparations including tablets, powders, capsules and the like, liquidpreparation such as injection preparations are preferred. The liquidpreparation may be provided in the form of a dried product which can beregenerated with use of water or other appropriate diluent on use.

The tablet and capsule can be subjected to an enteric coating accordingto an ordinary procedure. The enteric coating may be one ordinarilyemployed in this field. The capsule may contain either a solid or aliquid therein.

Where the pH sensitive drug and the pH sensitive drug composition are inthe form of a liquid preparation, the drug additives may include asolvent (e.g., a physiological saline solution, sterilized water, abuffer solution or the like), a membrane stabilizing agent (e.g.cholesterol or the like), a tonicity agent (e.g., sodium chloride,glucose, glycerin or the like), an antioxidant (e.g., tocopherol,ascorbic acid, glutathione or the like), a preservative (e.g.,chlorbutanol, paraben or the like) and the like. The solvent may be oneused for the preparation of the pH sensitive drug and pH sensitive drugcomposition.

Where the pH sensitive drug and the pH sensitive drug composition are inthe form of a solid preparation, the drug additives may include anexcipient (e.g., a sugar such as lactose, sucrose or the like, a starchsuch as corn starch, a cellulose such as crystalline cellulose, gumarabic, magnesium metasilicate aluminate, calcium phosphate or thelike), a lubricant (e.g., magnesium stearate, talc, polyethylene glycolor the like), a binder (e.g., mannitol, a sugar such as sucrose,crystalline cellulose, polyvinylpyrrolidone, hydroxypropylmethylcellulose or the like), a disintegrant (e.g., a starch such aspotato starch, a cellulose such as carboxymethylcellulose, crosslinkedpolyvinylpyrrolidone or the like), a colorant, a flavoring agent and thelike.

The pH sensitive drug and pH sensitive drug composition can be preparedby mixing with the above-mentioned drug additives as they are or afterfreeze-drying. Where the pH sensitive drug and pH sensitive drugcomposition are freeze-dried, it is possible to add an appropriate typeof diluent prior to the freeze-drying.

The administration form in case where the pH sensitive drug and the pHsensitive drug composition are used for treatment of a subject is notcritical, for which mention is made, for example, of oraladministration, and parenteral administration such as intravenousinjection, intraarterial injection, subcutaneous injection,intracutaneous injection, intramuscular injection, intraspinalinjection, percutaneous administration or percutaneous absorption. Forexample, where a peptide or protein is used as a physiologically activesubstance, administration via parenteral routes such as of subcutaneousinjection, intracutaneous injection, intramuscular injection andintravenous injection is possible. It will be noted that with respect tothe pH sensitive drug composition wherein a pH sensitive carrier and aphysiologically active substance are respectively independently mixed,it is possible to administer it in the form of local administration,particularly, subcutaneous injection, intracutaneous administration orintramuscular administration.

When the external environment of the pH sensitive drug and the sensitivedrug composition becomes lower than a physiological pH (e.g., pH 6.5)after administration to a subject, the membrane disruptive functionpromoting effect, or the membrane disruptive function promoting effectand the membrane fusion function promoting effect are developed, thusenabling a physiologically active substance to be specifically releasedin an efficient manner.

Thus, according to an illustrative embodiment, there is provided amethod for treating or preventing a disease including orally orperorally administering an effective amount of the above pH sensitivedrug or pH sensitive drug composition to a subject requiring thetreatment or prevention.

The subject can be a mammal, for example a human being.

As a disease, mention is made of, for example, cancers such as prostatecancer, lung cancer, colon cancer, liver cancer, stomach cancer, braincancer, breast cancer and the like, infection diseases such as HIV(Human Immunodeficiency Virus), hepatitis C, hepatitis B and the like,and central neurological diseases such as Alzheimer's disease,Parkinson's disease and the like.

More particularly, according to an illustrative embodiment, there isprovided a method for treating or preventing a disease.

Variations of the described embodiments are understood by those ofordinary skill in the relevant art.

In an illustrative embodiment, the pH sensitive drug and the pHsensitive drug composition can allow a physiologically active substanceto be directly transported to cells by culture. That is, according tothis embodiment, there is provided a culture method for transporting aphysiologically active substance to cells.

The culture method includes the step of culturing cells in a mediumcontaining a pH sensitive drug and/or a pH sensitive drug composition.

The pH sensitive drug and the pH sensitive drug composition are,respectively, those set out above. More particularly, there can bementioned a pH sensitive drug wherein a pH sensitive carrier supports atleast one physiologically active substance and a pH sensitive drugcomposition which independently contains a pH sensitive carrier and atleast one physiologically active substance therein. These may be usedsingly or in combination.

The medium is not critical and those known in the art may be used. Inparticular, mention is made of MEM, DMEM, RPMI and the like.

The amount of a pH sensitive drug and/or a pH sensitive drug compositionin the medium is not critical and the total molar concentration of a pHsensitive composition and an amphipathic substance is typically 0.73μmols/liter to 7.4 mmols/liter, for example 7.3 μmols/liter to 6.5mmols/liter, for example 8.0 μmols/liter to 4.2 mmols/liter.

The pH of the medium is typically not less than 7.0, for example 7.2 to7.8. If the pH of the medium is not less than 7.0, a pH sensitivecompound used as a constituent of the pH sensitive carrier can befavorably prevented from becoming unstable in the medium.

The types of cells are not critical and mention is made of cellscollected from a subject, established cultured cells and the like.

On this occasion, specific examples of the cells collected from asubject or established cultured cells include dendritic cells, NK(natural killer) cells, T-lymphocyte cells, B-lymphocyte cells andlymphocyte cells.

Of the above cells, it is possible to use cells collected from asubject. For example, dendritic cells, NK cells, T cells and lymphocytecells collected from a subject can be used.

Where cells collected from a subject are used, there can be obtainedcells of the subject through blood drawing, biopsy or the like.Accordingly, the culture method according to this embodiment may furtherinclude the step of collecting cells from a subject.

It will be noted that the cultured cells may be administered to asubject. In doing so, the disease of the subject can be treated orprevented. Hence, according to this embodiment, there is provided amethod for treating or preventing a disease.

In a further illustrative embodiment, the treating or preventing methodincludes the steps of collecting cells from a subject, culturing thecollected cells in a medium containing a pH sensitive drug and/or a pHsensitive drug composition, and administering the cultured cells to thesubject.

In this way, a disease can be treated or prevented. The disease is oneas mentioned hereinabove.

EXAMPLES

Illustrative examples are hereafter provided which should not beconstrued as limiting.

Starting Materials

In the examples, the following compounds were used. Where the name ofreagent and the name of product are the same, the name of product isomitted.

-   -   EYPC (non-hydrogenated egg yolk phosphatidylcholine: COATSOME        NC-50, made by NOF Corporation)    -   HSPC (soybean phosphatidylcholine: COATSOME NC-21, made by NOF        Corporation)    -   DDPC (1,2-decanoyl-sn-glycero-3-phosphatidylcholine: COATSOME        MC-1010, made by NOF Corporation)    -   DLPC (1,2-dilauroyl-sn-glycero-3-phosphatidylcholine: COATSOME        MC-1212, made by NOF Corporation)    -   DMPC (1,2-dimystiroyl-sn-glycero-3-phosphatidylcholine: COATSOME        MC-4040, made by NOF Corporation)    -   DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine: COATSOME        MC-6060, made by NOF Corporation)    -   DSPC (1,2-distearoyl-sn-glycero-3-phosphatidylcholine: COATSOME        MC-8080, made by NOF Corporation)    -   DOPC (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine: COATSOME MC        8181, made by NOF Corporation)    -   POPC (1-palmitoyl-2-oleoyl-sn-3-phosphatidylcholine: COATSOME MC        6081, made by NOF Corporation)    -   DLPE (1,2-dilauroyl-sn-glycero-3-phosphoethanolamine: COATSOME        ME 2020, made by NOF Corporation)    -   DMPE (1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine: COATSOME        ME 4040, made by NOF Corporation)    -   DSPE (1,2-distearoyl-sn-glycero-3-phosphoethanolamine: COATSOME        ME 8080, made by NOF Corporation)    -   DOPE (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine: COATSOME ME        8181, made by NOF Corporation)    -   Chems (Cholesteryl hemisuccinate: made by Nacalai Tesque Co.,        Ltd.)    -   NBD-PE        (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl)ammonium:        made by Avanti Polar Lipids, Inc.    -   Rh—PE (1,2-dioleoyl-sn-glycero-3-phoshoethanolamine-N-(lissamine        rhodamine B sulfonyl)ammonium: Avanti Polar Lipids, Inc.)    -   Sodium deoxycholate (Nacalai Tesque Co., Ltd.)    -   Sodium cholate (Nacalai Tesque Co., Ltd.)    -   Sodium ursodeoxycholate (Tokyo Chemical Industry Co., Ltd.)    -   Chenodeoxycholic acid (Tokyo Chemical Industry Co., Ltd.)    -   Hyodeoxycholic acid (Tokyo Chemical Industry Co., Ltd.)    -   Methyl cholate (Tokyo Chemical Industry Co., Ltd.)    -   Sodium dehydrocholate (Tokyo Chemical Industry Co., Ltd.)    -   Lithocholic acid (Nacalai Tesque Co., Ltd.)    -   Sodium glycocholate (Tokyo Chemical Industry Co., Ltd.)    -   Sodium taurocholate (Nacalai Tesque Co., Ltd.)    -   Sodium glycodeoxycholate (Nacalai Tesque Co., Ltd.)    -   Sodium taurodeoxycholate (Nacalai Tesque Co., Ltd.)    -   Sodium glycoursodeoxycholate (Nacalai Tesque Co., Ltd.)    -   Sodium tauroursodeoxycholate (Nacalai Tesque Co., Ltd.)    -   C27 bile acid (3α, 7α, 12α-Trihydroxycholestanoic acid: Avanti        Polar Lipids, Inc.)    -   5β-Cholanic acid (Sigma-Aldrich Co., LLC)    -   Monoammonium glycyrrhizinate (Tokyo Chemical Industry Co., Ltd.)    -   Glycyrrhizic acid (Nagara Science Co., Ltd.)    -   Sodium saccharin (Wako Pure Chemical Industries, Ltd.)    -   Methanol (Nacalai Tesque Co., Ltd.)    -   Chloroform (Wako Pure Chemical Industries, Ltd.)    -   Acetic acid (Wako Pure Chemical Industries, Ltd.)    -   Sodium acetate (Kanto Chemical Co., Inc.)    -   MES—Na (Merck & Co., Inc.)    -   HEPES—Na (Nacalai Tesque Co., Ltd.)    -   Sodium chloride (Kanto Chemical Co., Inc.)    -   Pyranine (Tokyo Chemical Industry Co., Ltd.)    -   DPX (p-xylene-bis-pyridinium bromide: Molecular Probes Inc.)    -   PBS (Phosphate Buffered Salts: PBS Tablets, made by Takara Bio        Inc.)    -   Polyoxyethylene sorbitan monofatty acid esters (Tween 20, 40,        60, 80, 65, 85: made by Tokyo Chemical Industry Co., Ltd.)    -   PEG-20-stearyl ether (polyoxyethylene 20-stearyl ester: made by        Wako Pure Chemical Industries, Ltd.)    -   PEG-23-lauryl ether (polyoxyethylene 23-lauryl ester: made by        Wako Pure Chemical Industries, Ltd.)    -   Sorbitan fatty acid esters (SPAN 20: sorbitan monolaurate, made        by Nacalai Tesque Co., Ltd., SPAN 40, 60: made by Tokyo Chemical        Industry Co., Ltd., SPAN        80: sorbitan monooleate, made by Nacalai Tesque Co., Ltd.,        65: sorbitan tristearate, made by Wako Pure Chemical Industries,        Ltd., SPAN 85: made by Tokyo Chemical Industry Co., Ltd.)    -   Glycerol monocaprate (Monocaprin, made by Tokyo Chemical        Industry Co., Ltd.)    -   Glycerol monocaprylate (Monocaprylin, made by Tokyo Chemical        Industry Co., Ltd.)    -   Glycerol monolaurate (Monolaurin, made by Tokyo Chemical        Industry Co., Ltd.)    -   Glycerol monomyristate (Monomyristin, made by Tokyo Chemical        Industry Co., Ltd.)    -   Glycerol monopalmitate (Monopalmitin, made by Tokyo Chemical        Industry Co., Ltd.)    -   Glycerol monostearate (Monostearin, made by Tokyo Chemical        Industry Co., Ltd.)    -   Glycerol monooleate (Monoolein, made by Tokyo Chemical Industry        Co., Ltd.)    -   Glycerol dilaurate (α,α Dilaurin, made by Tokyo Chemical        Industry Co., Ltd.)    -   Glycerol distearate (made by Wako Pure Chemical Industries,        Ltd.)    -   Glycerol dioleate (made by Wako Pure Chemical Industries, Ltd.)    -   Polyoxyethylene castor oil (Polyoxyethylene 10 castor oil, made        by Wako Pure Chemical Industries, Ltd.)    -   Polyoxyethylene hardened castor oil (10: polyoxyethylene 10        hardened castor oil, made by Wako Pure Chemical Industries,        Ltd., 40: Uniox HC-40, made by NOF Corporation, 60: Uniox HC-60,        made by NOF Corporation)    -   1-Butanol (made by Nacalai Tesque Co., Ltd.)    -   1-Octanol (made by Nacalai Tesque Co., Ltd.)    -   1-Dodecanol (made by Tokyo Chemical Industry Co., Ltd.)    -   1-Hexadecanol (made by Nacalai Tesque Co., Ltd.)    -   1-Eicosanol (made by Tokyo Chemical Industry Co., Ltd.)    -   Lauric acid (made by Nacalai Tesque Co., Ltd.)    -   Sodium oleate (made by Nacalai Tesque Co., Ltd.)    -   Ethyl octenoate (made by Nacalai Tesque Co., Ltd.)    -   Ethyl laurate (made by Tokyo Chemical Industry Co., Ltd.)    -   Ethyl oleate (made by Nacalai Tesque Co., Ltd.)    -   Lactose (made by Nacalai Tesque Co., Ltd.)    -   L-leucine (made by Nacalai Tesque Co., Ltd.)    -   L-histidine (made by Nacalai Tesque Co., Ltd.)    -   Soybean oil (soybean oil, made by Nacalai Tesque Co., Ltd.)    -   Squalane (made by Nacalai Tesque Co., Ltd.)    -   Squalene (made by Nacalai Tesque Co., Ltd.)    -   α-Tocopherol (DL-α-tocopherol, made by Nacalai Tesque Co., Ltd.)    -   Tocopherol acetate (DL-α-tocopherol acetate, made by Nacalai        Tesque Co., Ltd.)    -   Benzyl benzoate (made by Nacalai Tesque Co., Ltd.)    -   Benzyl paraoxybenzoate (made by Tokyo Chemical Industry Co.,        Ltd.)    -   Ascorbyl palmitate (made by LKT Laboratories, Inc.)    -   Gum arabic (gum arabic powder, made by Nacalai Tesque Co., Ltd.)    -   Gelatin (gelatin purified powder, made by Nacalai Tesque Co.,        Ltd.)    -   Cyclodextrin (made by Nacalai Tesque Co., Ltd.)    -   Methylcellulose (made by Nacalai Tesque Co., Ltd.)    -   Mineral oil (made by Nacalai Tesque Co., Ltd.)    -   Paraffin (made by Nacalai Tesque Co., Ltd.)    -   Sodium hydroxide aqueous solution (0.1 mol/liter: made by        Nacalai Tesque Co., Ltd.)    -   Hydrochloric acid (0.1 mol/liter 1 mol/liter: made by Nacalai        Tesque Co., Ltd.)    -   Triton-X100 (Triton X100, made by Wako Pure Chemical Industries,        Ltd.)    -   Model peptide: OVA257-264 (SIINFEKL, prepared by commission to        PH Japan Co., Ltd.)    -   Fluorescence-labeled peptide: OVA257-264-Rh (prepared by        commission to PH Japan Co., Ltd.)    -   Model protein: OVA (Sigma-Aldrich Inc.)    -   Trypsin (made by Life Technologies Inc.)    -   EDTA (ethylenediamine tetraacetate, made by Nacalai Tesque Co.,        Ltd.)    -   β-gal (β-D-galactosidase, made by Wako Pure Chemical Industries,        Ltd.)    -   FBS (Fetal bovine serum: made by Kokusan Chemical Co., Ltd.)    -   MEM (Minimum Essential Medium: Eagle's MEM and        L-glutamine-containing solution, made by Nacalai Tesque Co.,        Ltd.)    -   DMEM without Phenol Red (solution of 4.5 g/l of Dulbecco's        Modified Eagle Medium (DMEM) without containing glucose,        L-glutamine, pyruvic acid and phenol red)    -   DMEN (Dulbecco's Modified Eagle Medium, made by Nacalai Tesque        Co., Ltd.)    -   Chloroquine diphosphate (made by Nacalai Tesque Co., Ltd.)    -   IsoFlow (made by Beckman Coulter Inc.)

Preparation of Samples Preparation of pH Sensitive Carriers

1000 nmol of an amphipathic substance dissolved in methanol (orchloroform) and a pH sensitive compound or candidate compound dissolvedin methanol (or chloroform) were mixed in a 10 mL eggplant flask andconverted to a thin film by means of a rotary evaporator (BuCHI). Itwill be noted that the ratio between the amphipathic substance and thepH sensitive compound or candidate compound was so set as to providedesired ratios (molar ratios of 100:10, 100:20, 100:640, etc.). Where aplurality of amphipathic substances were used, the amphipathicsubstances were so controlled in total amount to have the number ofmoles desired (1000 nmol). 1 mL of an MES buffer (MES: 25 mM, NaCl: 125mM, pH 7.4) was added to the resulting thin film, followed by dispersionby one-minute irradiation with ultrasonic waves at a normal temperatureby use of an ultrasonic irradiator (USC-J) to obtain an aqueous solutionof an intended pH sensitive carrier (a dispersion of the carrier).

Preparation of Carriers for Comparison (EYPC Alone and DLPC Alone)

1000 nmol of EYPC or DLPC dissolved in chloroform was placed in a 10 mLeggplant flask, followed by conversion to a thin film by means of arotary evaporator (BuCHI). 1 mL of an MES buffer (MWS: 25 mM, NaCl: 125mM, pH 7.4) was added to the resulting thin film, followed by dispersionby one-minute irradiation with ultrasonic waves at a normal temperatureby use of a ultrasonic irradiator (USC-J) to obtain a dispersion of EYPCalone or DLPC alone.

Carriers Containing Macromolecular Materials

In a similar way as in the preparation procedure of the pH sensitivecarrier, a thin film of a pH sensitive compound and a macromolecularmaterial was prepared to provide a carrier. The macromolecular material,such as gum arabic, gelatin, methylcellulose, mineral oil or paraffin,was used in amounts of 1/5 times, one time and five times the weight ofthe 1600 nmol of the pH sensitive compound.

(pH Sensitive Liposomes)

In a similar way as in the preparation procedure of the pH sensitivecarrier, a thin film of DOPE and Chems or oleic acid was prepared toprovide a liposome. It will be noted that the DOPE-Chems (DOPE:Chems=3:2(by molar ratio)) and the DOPE-oleic acid ((DOPE:oleic acid=7:3 (bymolar ratio)), which were, respectively, a pH sensitive liposome, wereprepared using 1000 nmol of DOPE, a given amount of Chems or oleic acidand 1 mL of an MES buffer (MES: 25 mM, NaCl: 125 mM, pH 7.4).

Preparation of a peptide-containing carrier and a protein-containingcarrier 0 to 1536 μg of OVA257-264 (SIINFEKL) model peptide or an OVAmodel protein per 1000 nmol of an amphipathic substance was weighed anddissolved in 1 mL of an MES buffer (MES: 25 mM, NaCl: 125 mM, pH 7.4).These solutions were used to prepare the respective carriers, from whichthere was obtained a dispersion containing the peptide or protein.

With the case using an OVA257-264-Rh fluorescence-labeled peptide,preparation was made using 140 μg of the fluorescence-labeled peptideper 1000 nmol of the amphipathic substance, and with the case usingβ-gal, 1.4 mg of β-gal per 1000 nmol of the amphipathic substance wasused for the preparation.

Measuring Method Measurement of Transmittance

250 μL of a carrier dispersion was added to 250 μL of an MES buffer(MES: 25 mM, NaCl: 125 mM, pH 7.4) to provide a solution formeasurement. Using UV-2450, a transmittance at 500 nm was measured at anormal temperature.

Measurement of Zeta Potential and Particle Size

For the measurement of the zeta potential, 20 to 50 μL of a carrierdispersion was added to 1.0 mL of a HEPES buffer (HEPES: 1.0 mM) whosepH was adjusted to 7.4 to provide a solution for the measurement. Themeasurement was carried out plural times using Nano ZS 90 and theresulting values of zeta potential were averaged to obtain a zetapotential of the carrier particles.

Measurement of Particle Size and Polydispersity Index

For the measurement of the particle size and polydispersity index (PDI:Polydispersity Index), an appropriate amount of a carrier dispersion wasadded to an MES buffer (MES: 25 mM, NaCl: 125 mM, pH 7.4) to provide asolution for measurement. The measurement was carried out plural timesby use of Nano ZS 90 and the values of Z-average (radius) obtained bydynamic light scattering measurement were averaged and its double valuewas provided as a Diameter (diameter or particle size). The value of PDIwas determined by averaging the values of PDI obtained by pluralmeasurements.

Leaching Test: Measurement of a Leakage (Leaching Rate)

The leakage (leaching rate) was determined according to the methoddescribed by K. Kono et al., Bioconjugate Chem., 2008 19 1040-1048 andevaluated using an EYPC liposome including Pyranine serving as afluorescent substance and DPX serving as a quencher.

3000 nmol of EYPC dissolved in chloroform was measured and placed in a10 mL eggplant flask and converted to a thin film by use of a rotaryevaporator (BuCHI). 500 μL of a Pyranine solution (Pyranine: 35 mM, DPX:50 mM, MES: 25 mM, pH 7.4) was added, followed by dispersion with use ofan ultrasonic irradiator (USC-J) and passage through a polycarbonatefilm having a pore size of 100 nm by use of an extruder to obtain auniform particle size. Using an MES buffer (MES: 25 mM, NaCl: 125 mM, pH7.4) and a G100 column, an outer water layer was substituted to obtain adispersion of EYPC liposomes including the fluorescent substance. Theconcentration of the choline group of the phospholipid was determined byuse of the phospholipid C test Wako and was adjusted by use of an MESbuffer (MES: 25 mM, NaCl: 125 mM, pH 7.4) in such a way as to obtain 1.0mmol/L of the phospholipid. 20 μL of the EYPC liposome dispersion whoseconcentration had been adjusted, and 20 μL of an evaluation sampledispersion such as of a carrier or a pH sensitive compound alone, anamphipathic substance alone or the like were charged into 2960 μL of therespective MES buffers (MES: 25 mM, NaCl: 125 mM) which were prepared tohave different pHs. After incubation at 37° C. for 30 minutes or 90minutes (in examples, the results of 90 minutes were shown unlessotherwise indicated), fluorescences at Ex 416 and Em 512 nm wereobserved by use of spectrophotometer FP-6500 to monitor the leakage. TheDOPE-Chems and DOPE-oleic acid were, respectively, measured in an aceticacid buffer (acetic acid: 25 mM, NaCl: 125 mM).

With respect to other samples, measurement at a pH of 4.0 to 3.0 wascarried out by use of an acetic acid buffer.

It will be noted that the leakage was calculated in such a way that incase where the EYPC liposome dispersion alone was used, it was taken as0% and a value obtained in case where 30 μL of a 10-fold dilutedTriton-X100 was added was taken as 100%.

More particularly, the leakage was calculated according to the followingequation. In the following equation, a measured fluorescence intensityis represented by L, a fluorescence intensity of a dispersion alone ofEYPC liposomes including a fluorescent substance is represented by L₀,and a fluorescence intensity in case where Triton-X100 was added isrepresented by L₁₀₀.

Leakage(%)=(L−L ₀)/(L ₁₀₀ −L ₀)×100

Fusion Test: Measurement of Fusion (Membrane Fusion)

The fusion (membrane fusion) was carried out according to the methoddescribed by K. Kono et al., Biomaterials 2008 29 4029-4036 andevaluated by use of FRET (Fluorescence Resonance Energy Transfer). Forthe fluorescent labeling, NBD-PE and Rh—PE were used.

A thin film of EYPC (1000 nmol of EYPC) containing 0.6 mol % of NBD-PEand Rh—PR relative to EYPC was prepared and added to 1 mL of an MESbuffer (MES: 25 mM, NaCl: 125 mM, pH 7.4), followed by dispersion withuse of a ultrasonic irradiator (USC-J) and passage through apolycarbonate film having a pore size of 100 nm by use of an extruder toobtain a double fluorescence-labeled EYPC liposome dispersion. 20 μL ofthe double fluorescence-labeled EYPC liposome dispersion and 20 μL of anevaluation sample dispersion such as of a carrier or a pH sensitivecompound alone, an amphipathic compound alone or the like were chargedinto 2960 μL of MES buffers (MES: 25 mM, NaCl: 125 mM) which wereadjusted to different pHs and incubated at 37° C. for 60 minutes,followed by measurement of fluorescent spectra at 500 nm to 620 nm bymeans of excitation light of 450 nm by use of a spectrophotometer(EP-6500) to obtain a fluorescent intensity ratio between 520 nm and 580nm.

The fusion rate was calculated such that the fluorescent intensity ratioin case where the double fluorescence-labeled EYPC liposome dispersionobtained above and an amphipathic substance were incubated was taken as0% and the ratio in case where the double fluorescence-labeled EYPCliposome dispersion and a dispersion of a pH sensitive carrier or anamphipathic substance were subjected to methanol treatment was taken as100%. The methanol treatment was carried out in such a way that both ofthe double fluorescence-labeled EYPC liposome dispersion and anevaluation sample dispersion such as of a pH sensitive carrier or a pHsensitive compound alone, an amphipathic compound alone or the like weredissolved in methanol and converted to a thin film by use of a rotaryevaporator (BuCHI), followed by dispersion by use of 3.0 mL of an MESbuffer (MES: 25 mM, NaCl: 125 mM) and an ultrasonic irradiator (USC-J).

More particularly, the fusion rate was calculated according to thefollowing equation. It will be noted that in the following equation, afluorescence intensity ratio obtained by the measurement is representedby R, a fluorescence intensity ratio obtained where the doublefluorescence-labeled EYPC liposome dispersion and an amphipathicsubstance were incubated is represented by R₀ and a fluorescenceintensity ratio obtained where double fluorescence-labeled EYPC liposomedispersion and an evaluation sample dispersion such as of a carrier, ora pH sensitive compound alone, an amphipathic compound alone or the likewere subjected to methanol treatment is represented by R₁₀₀.

Fusion rate(%)=(R−R ₀)/(R ₁₀₀ −R ₀)×100

Confirmation of Membrane Fusion Against Cell Membrane

It was confirmed by use of HeLa cells that a pH sensitive carrierinduced membrane fusion with an actual cell membrane.

On the day before administration of a pH sensitive carrier, HeLa cellswere spread on a matsunami glass bottom dish and cultured with 10%FBS-containing DMEM. On this occasion, the culture was carried out byuse of an incubator (MCO20AIC) set at 5% CO₂ and 37° C. After theincubation, the cells were washed with 10% FBS-containing DMEM. Next,2.0 mL of DMEM whose pH was adjusted to 7.4 by use of a sodium hydroxideaqueous solution or hydrochloric acid and which contained 25 mM of Hepesand 50 μM of chloroquine diphosphate was added to the cells, followed byone hour pre-incubation.

It will be noted that in case where a test was carried out at a pH of5.3, 2.0 mL of DMEM whose pH was adjusted to 5.3 by use of a sodiumhydroxide aqueous solution or hydrochloric acid and which contained 25mM of MES and 50 μM of chloroquine diphosphate was added to the cells,followed by one hour pre-incubation. After the pre-incubation, 100 μL ofa dispersion of 0.6 mol %, relative to an amphipathic substance, of anRh—PE fluorescence-labeled pH sensitive carrier was added to a mediumadjusted to a given pH, followed by two hours of incubation. The cellswere rinsed at least three times with phenol red-free DMEM and observedthrough a fluorescence microscope (Axiovert 200M-soft: Axio vision3.0-light source: Fluo Arc). It is to be noted that the fluorescenceintensity of the cells was evaluated by use of a flow cytometer(Cytomics FC500, soft: CXP version 2) after the rinsed cells had beenharvested with PBS containing 0.025 wt % of trypsin and 0.01 wt % ofEDTA.

Evaluation of Cytosolic Delivery Using a Fluorescence-Labeled Peptide

OVA-257-264-Rh was chosen as a model peptide. 140 μg/ml of afluorescence-labeled peptide solution was prepared by use of PBS passedthrough a 0.22 μm filter and used for the preparation of a carrier.Cells used were RAW cells, and culture was carried out by use of anincubator (MCO20AIC) set at 5% CO₂ and 37° C. The RAW cells were spreadon a matsunami glass bottom dish on the day before the charge of thecarrier and cultured in a 10% FBS-containing MEM medium.

After rinsing the cells with PBS, the medium was substituted with 1900μL of a fresh 10% FBS-containing MEM medium, into which 100 μL of therespective samples was charged. Incubation was continued over 16 to 20hours and the cells were rinsed at least three times with PBS.Thereafter, 2 mL of a fresh 10% FBS-containing MEM medium was added,following by three hours post-incubation. The cells were rinsed withPBS, followed by substitution with a DMEM-without-Phenol-Red medium andobservation of the cells through a fluorescence microscope

Axiovert 200M-soft: Axio vision 3.0-light source: Fluo Arc(cytosolic delivery of β-gal)

Using PBS passed through a 0.22 μm filter, there was prepared a 1.4mg/mL of β-gal solution. A mixed thin film made up of 1000 nmol of DLPCand 1600 nmol of deoxycholic acid or ursodeoxycholic acid was dispersedin the thus prepared 6-gal solution to prepare a β-gal-containingcarrier. On the day before charge, the RAW cells were spread on amatsunami glass bottom dish and cultured, and the cells were rinsed withPBS immediately before charge. The culture was carried out by use of anincubator (MCO 20 AIC) set at 5% CO₂ and 37° C. and a 10% FBS-containingMEM medium. After substitution with 1900 μL of a fresh 10%FBS-containing MEM medium, 100 μL of the respective samples was charged,followed by 16 to 20 hours incubation. The cells were rinsed at leastthree times with PBS. Thereafter, 2 mL of a fresh 10% FBS-containing MEMmedium was added, following by three hours post-incubation. The cellswere rinsed with PBS, followed by staining the cells with use of aβ-Galactosidase Staining Kit (purchased from Takara Bio Inc.), andobserving the cells through a microscope (Axiovert 200M-soft: Axiovision 3.0). The staining was carried out in accordance with therecommendation of the kit.

Evaluation of Cytosolic Delivery in the Case where a pH SensitiveCarrier and a Physiologically Active Substance were, Respectively UsedIndependently

On the previous day, RAW cells were spread on a matsunami glass bottomdish and cultured with 10% FBS-containing MEM. After rinsing with PBS,MEM was added, followed by a one hour incubation. 1900 μL of MEMcontaining fluorescence-labeled peptide-FITC or fluorescence-labeledOVA-FITC at a concentration of 30 μg/mL was prepared and substitutedwith the culture medium. Moreover, a solution of 100 μL of a pHsensitive carrier was added, followed by 16 to 20 hours of incubation inthe culture medium in such a state that both were mixed. It was alreadyconfirmed that the fluorescence-labeled peptide-FITC andfluorescence-labeled OVA-FITC were each not supported with the pHsensitive carrier in a mixed state with a pH sensitivecarrier-containing solution. After rinsing with PBS and three hourspost-incubation with 2 mL of fresh MEM, the cells were rinsed with PBS,followed by substitution with phenol red-free DMEM and observationthrough a fluorescence microscope. The culture was carried out by use ofan incubator (MCO20AIC) set at 5% CO₂ and 37° C. and the cells wereobserved through a fluorescence microscope (Axiovert 200M-soft: Axiovision 3.0-light source: Fluo Arc).

(1) Complexing of Deoxycholic Acid

Initially, complexing of deoxycholic acid and amphipathic substances wasevaluated.

According to the preparation of the foregoing pH sensitive carrier,mixed thin films of 1000 nmol of EYPC or DLPC and different amounts (0to 6400 nmol) of deoxycholic acid were prepared, to which 1 mL of an MESbuffer with a pH of 7.4 was added and irradiated with ultrasonic waves,thereby preparing deoxycholate complexed dispersions. A photograph ofthe dispersions containing EYPC and deoxycholic acid wherein deoxycholicacid was contained in different amounts is shown in FIG. 2A and aphotograph of the dispersions containing DLPC and deoxycholic acidwherein deoxycholic acid was contained in different amounts is shown inFIG. 2B. It will be noted that FIGS. 2A and 2B, respectively, showdispersions of 1000 nmol of the lipids containing, as viewed from theleft side thereof, 0 nmol, 50 nmol, 100 nmol, 200 nmol, 400 nmol, 800nmol, 1600 nmol, 3200 nmol and 6400 nmol of deoxycholic acid. In eitherlipid of EYPC or DLPC, a dispersion of the lipid alone became clouded,whereas the solutions of complexed deoxylate were found to becomeclearer depending on the amount of the acid being complexed.

The transmittance of the respective dispersions at 500 nm was measured,resulting in a tendency similar to that obtained by visual observation.FIG. 2C shows the results of measurement of a transmittance ofdispersions containing EYPC and deoxycholic acid and FIG. 2D shows theresults of measurement of a transmittance of dispersions containing DLPCand deoxycholic acid. These results suggest the formation of complexes(associated products) of deoxycholic acid and the lipids. The complex ofdeoxycholic acid and a lipid may sometimes hereinafter referred to as“lipid-deoxycholate complex.”

Next, the zeta potential of these dispersions was checked. In FIG. 3,there are shown the results of measurement of a zeta potential of adispersion containing EYPC and deoxycholic acid (i.e. EYPC-deoxycholatecomplex in the figure) and a dispersion containing DLPC and deoxycholicacid (i.e. DLPC-deoxycholate complex in the figure) relative to theamount of deoxycholic acid. It will be noted that the results of FIG. 3show an average value of five different measurements and ± is SD(standard deviation).

Both types of dispersions had the values negatively lowered inassociation with the complexing of deoxycholic acid. This means thecomplexing of deoxycholic acid having a negative charge with the lipidand indicates the formation of a mixed complex of deoxycholic acid andthe lipid. In the case using either of the lipids, the zeta potentialshowed a value of about −30 mV in an amount of 1600 nmol of deoxycholicacid being complexed and the zeta potential value did not lowerappreciably in larger amounts used for the complexing. Thus, it isconsidered that deoxycholic acid is so complexed as to substantiallycover the surface of the resulting complex therewith in the amountindicated above.

(2) Complex Structure

According to the preparation of the pH sensitive carrier, a fluorescentsubstance-holding test (a test of dispersing a thin film by use of aPyranine solution) of the complex prepared from 1600 nmol of deoxycholicacid relative to 1000 nmol of DLPC was carried out, revealing that thefluorescent substance was not held by the complex. Since the complexcould not hold the fluorescent substance, it was suggested that thecomplex did not have a hollow structure, but was in micellar form (datanot shown).

Next, the particle size of different types of complexes obtainedaccording to the preparation of the pH sensitive carrier was measured.The results of measuring the particle size by the dynamic lightscattering method revealed that the particle size (Diameter) of theEYPC-deoxycholate complex (EYPC:deoxycholic acid=1000 nmol:1600 nmol)was at about 73 nm and the particle size (Diameter) of theDLPC-deoxycholate complex (DLPC:deoxycholic acid=1000 nmol:1600 nmol)was at about 43 nm (Table 1). The polydispersity indices (PDI) of thesecomplexes were, respectively, values as small as 0.26 and 0.07,demonstrating that the complexes of deoxycholic acid and the lipids werein the form of small-sized, uniform particles, respectively.

TABLE 1 Particle size and PDIs Diameter (nm) PDI EYPC only   411 ± 10.60.48 ± 0.03 DLPC only  306 ± 5.6 0.47 ± 0.03 EYPC-deoxycholate 73.1 ±0.5 0.26 ± 0.01 DLPC-deoxycholate 43.1 ± 0.5 0.07 ± 0.01 The values areeach an average value of five different measurements, and ± indicatesSD. EYPC only: EYPC alone DLPC only: DLPC alone EYPC-deoxycholate:EYPC-deoxycholate complex DLPC-deoxycholic acid: DLPC-deoxycholatecomplex

(3) pH Sensitivity (Leaching Test)

The pH sensitivities of EYPC alone, DLPC alone, EYPC-deoxycholatecomplex and DLPC-deoxycholate acid complex were checked. The test wascarried out in such a way that a complex was prepared according to theforegoing preparation method of carrier using 1000 nmol of a lipid (EYPCor DLPC) and 1600 nmol of deoxycholic acid, followed by incubation withEYPC liposome which is a model of biological membrane according to theforegoing method for the leaching test (unless otherwise indicated, theleaching test was one resulting from 90 minutes incubation herein andwhenever it appears hereinafter). FIG. 4 shows the results ofmeasurement of the leakages of EYPC alone, DLPC alone, deoxycholic acidalone, EYPC-deoxycholate complex and DLPC-deoxycholate complex at pHs of7.4, 6.5, 6.0, 5.5, 5.0 and 4.5. The plots in FIG. 4 are, respectively,an average value of three different measurements, and ± is SD.

EYPC alone, DLPC alone and the EYPC-deoxycholate complex did not causethe leakage of the fluorescent substance at any of pHs of from 7.4 to4.5 and thus, showed no pH sensitivity, whereas the DLPC-deoxycholatecomplex caused a greater degree of leakage than deoxycholic acid aloneat a pH not higher than 6.5. Thus, it was clarified that theDLPC-deoxycholate complex developed a pH sensitive, membrane disruptivefunction promoting effect.

According to this test, it was revealed that there could be obtainedcomplexes obtained from the combinations of deoxycholic acid andappropriate types of amphipathic substances and capable of developingthe function in response to a weakly acidic environment. The pH for thedevelopment of the effect was at not higher than 6.5 and was in a pHrange enough for practical use. Since no leakage was caused at a pH inthe physiological environment, the pH sensitivity was such that thefunction was well controlled in on-off fashion.

(Membrane Fusion Test)

For delivering a physiologically active substance to cellular cytosol,it is desirable to have the function of membrane fusion in a weaklyacidic environment. According to the method for the foregoing membranefusion test, a double fluorescence-labeled EYPC liposome and the carrier(complex) prepared by use of 1000 nmol of a lipid (EYPC or DLPC) and1600 nmol of deoxycholic acid were subjected to 60 minutes incubation at37° C. at different pHs to check the fusion of both. FIG. 5(A) is agraph showing fluorescence intensity ratios of EYPC alone, DLPC alone,deoxycholic acid alone, EYPC-deoxycholate complex and DLPC-deoxycholatecomplex at pHs of 7.4, 6.5, 6.0, 5.5, 5.0 and 4.5. FIG. 5(B) is a graphshowing, at the same pHs as indicated above, fusion rates of deoxycholicacid alone, EYPC-deoxycholate complex and DLPC-deoxycholate complex. Thefusion rate of 0% is a fluorescence intensity ratio in case where DLPCalone or EYPC alone was added to the double fluorescence-labeledliposome and 100% indicates a value obtained by subjecting therespective samples to methanol treatment. The value of deoxycholic acidalone was calculated using a value of the double fluorescence-labeledliposome taken as 0% and a value of methanol-treated EYPC-deoxycholicacid taken as 100%. It will be noted that the plots in FIGS. 5(A) and5(B) are each an average value of three different measurements, and ± isSD.

From the results of FIG. 5(A), it will be seen that theDLPC-deoxycholate complex increased the fluorescence intensity ratio inassociation with the lowering of pH and caused the fusion with thedouble fluorescence-labeled EYPC liposome. The evaluation of thesefusion rates revealed that the DLPC-deoxycholate complex developed amembrane fusion function promoting effect in a weakly acidic environment(FIG. 5(B)). The DLPC-deoxycholate complex developed both the membranedisruptive function promoting effect and the membrane fusion functionpromoting effect. In view of this, it is considered that both effectsare derived from the same phenomena, with the possibility that a carriercapable of developing the membrane disruptive function promoting effectalso develops the membrane fusion function promoting effect.

It will be noted that the fluorescence intensity ratio at a pH of 5.0indicated a value of about 80% of the sample subjected to methanoltreatment (FIG. 5(A)). The methanol-treated sample is in a state ofcomplete fusion between the double fluorescence-labeled liposome and thecarrier, suggesting that the EYPC liposome of the biological membranemodel and the prepared carrier are fused in high efficiency. Thus,highly efficient delivery of a physiologically active substance will beexpected.

(4) Comparison with Ordinary pH Sensitive Liposomes

In order to confirm the degree of pH sensitivity and leaching strength,comparison with DOPE-Chems liposome (DOPE:Chems=3:2 (by molar ratio))and DOPE-oleic acid liposome (DOPE:oleic acid=7:3 (by molar ratio)),both of which are well known as a pH sensitive liposome, was carried outaccording to the leaching test. A dispersion containing a DOPE-Chemsliposome or DOPE-oleic acid liposome in an amount corresponding to 20nmol of DOPE was used for measurement. FIG. 6 is a graph showing theleakages of the DOPE-Chems liposome, DOPE-oleic acid liposome andDLPC-deoxycholate complex at different pHs. The plots of FIG. 6 are eachan average of three measurements and ± is SD.

With respect to the DOPE-Chems liposome and the DOPE-oleic acidliposome, leakage started to occur at a pH of not higher than 6.0 and aleakage of 20 to 30%, which was maximum in value, was indicated at a pHof 3.5. On the other hand, the pH sensitive carrier (DLPC-deoxycholatecomplex) commenced to induce leakage from a pH of 6.5 and its leakage ofover 60% was obtained.

The leakage of the DLPC-deoxycholate complex was higher than those ofthe existing pH sensitive liposomes, revealing that the illustrative pHsensitive carrier (DLPC-deoxycholate complex) has a strong effect ofinstabilizing and disrupting the membrane. It has been shown that the pHat which the effect is developed is closer to neutral and thus, thecarrier is highly sensitive to a weakly acidic environment.

(5) Investigation of the Complexing Amount of Deoxycholic Acid

In order to check the complexing amount of deoxycholic acid necessaryfor the development of the effect, different amounts of deoxycholic acidwere used for the preparation of pH sensitive carriers to evaluate thedevelopment of the membrane fusion function promoting effect accordingto the membrane fusion test.

Measurement was repeated three times to calculate an average value andSD. The value of deoxycholic acid alone was calculated by using a valueof a methanol-treated EYPC-deoxycholate complex. FIGS. 7(A) and 7(B),respectively, show a fusion rate of each of deoxycholic acid alone,EYPC-deoxycholate complex and DLPC-deoxycholate complex relative to theamount of deoxycholic acid.

From FIGS. 7(A) and 7(B), it can be understood that the preparedcarriers exhibit a larger value than deoxycholic acid alone in acomplexing amount of not less than 100 nmol and are able to develop themembrane fusion function promoting effect. It can also be understoodthat the development of the membrane fusion function promoting effectcan be obtained by complexing 100 to 6400 nmol of deoxycholic acid with1000 nmol of the lipid.

It will be noted that the fusion rate of the EYPC-deoxycholate complexis substantially the same value as with deoxycholic acid alone, thusshowing that the EPYC-deoxycholate complex has not acquired the membranefusion function promoting effect as a result of complexing with the pHsensitive compound.

(6) Influence of Lipid Structure

From the above investigation, it has been made clear that whendeoxycholic acid and an appropriate type of lipid (amphipathicsubstance) are combined, there can be obtained a carrier that is able todevelop the membrane disruptive function promoting effect and themembrane fusion function promoting effect in a weakly acidicenvironment. For the purpose of elucidating the type of lipid capable ofyielding these properties, a number of carriers were prepared withlipids having a variety of structures and subjected to the leaching testor membrane fusion test.

As to the lipid structure, the influences of the length of the acylgroup (10 to 18 carbon atoms) of diacylphosphatidylcholines and theunsaturated bond of the acyl group of diacylphosphatidylcholines werechecked. The respective carriers were prepared using 1000 nmol of lipidsand 1600 nmol of deoxycholic acid. Measurement was repeated three times,from which an average value and SD were calculated, respectively. Itwill be noted that the “number of carbon atoms” of amphipathic substancemeans the number of carbon atoms of a fatty acid moiety (acyl group)serving as the hydrophobic site of the amphipathic substance.

FIG. 8(A) shows the fusion rate of each of deoxycholic acid alone,DSPC-deoxycholate complex, DPPC-deoxycholate complex, DMPC-deoxycholatecomplex, DLPC-deoxycholate complex and DDPC-deoxycholate complex. FIG.8(B) shows the fusion rate of each of deoxycholic acid alone,HSPC-deoxycholate complex, DOPC-deoxycholate complex andPOPC-deoxycholate complex.

From FIG. 8(A), it will be seen the carriers using DSPC, DPPC and DMPChave similar values to deoxycholic acid alone and no effect was thusshown, whereas DLPC and DDPC showed the effect. It is considered thatthe carbon length of the lipids provides an influence and thedevelopment of the effect is obtained when using lipids having a shortcarbon chain. A lipid having a short carbon chain is likely to generatea flip flop that is the inversion motion of the molecule in themembrane, and this nature is considered to influence the development.

As to the influence of the unsaturated bond, the carriers using POPChaving one unsaturated bond and DOPC having two unsaturated bonds in thechain with 18 carbon atoms did not develop any effect (FIG. 8(B)). Thus,it is shown that the unsaturated bond does not provide an appreciableinfluence on the development of the effect.

Next, the influence of the head structure of lipid on the development ofthe effect was checked. Carriers were prepared using 1000 nmol of lipidsand 1600 nmol of deoxycholic acid, respectively. Measurement wasrepeated three times, from which an average value and SD werecalculated, respectively.

FIG. 9(A) is a graph showing the leakage of each of deoxycholic acidalone, DLPE alone, DMPE alone, DSPE alone and DOPE alone, and FIG. 9(B)is a graph showing the leakage of each of deoxycholic acid alone,DLPE-deoxycholate complex, DMPE-deoxycholate complex, DSPE-deoxycholatecomplex and DOPE-deoxycholate complex.

None of the lipids having PE resulted in the development of the effect,revealing that the choline group is preferred as the head structure(FIGS. 9(A) and 9(B)).

From the above results, it has been demonstrated that for an amphipathicsubstance capable of yielding the development of the effect, it ispreferred to use unsaturated or saturated lipids having a choline groupas a head structure and having a chain of 10 to 12 carbon atoms.

(7) Investigation of Other Types of Amphipathic Substances

Substances other than lipid have been utilized for the delivery of thephysiologically active substance. Moreover, it is known that deoxycholicacid forms complexes with hydrophobic substances other than a lipid,with the possibility that there can be obtained carriers havingfunctions in association with a variety of substances. To this end, avariety of substances and deoxycholic acid were complexed to preparecarriers, which were evaluated by the leaching test. Since deoxycholicacid alone invites an increasing leakage by the action of its surfaceactivity, screening was carried out in such a way that a substance thatis able to yield the development of the effect is defined to satisfyboth of the requirements: (1) in the leaching test, a leakage at a givenpH of less than a physiological pH increases over a leakage at thephysiological pH and its increase increment is larger than an increaseincrement obtained in case where a pH sensitive compound alone is usedfor the test; and (2) in a leaching test at a given pH less than thephysiological pH, a leakage at the time when a complex (pH sensitivecarrier) is formed from a pH sensitive compound and an amphipathicsubstance is larger than the sum of a leakage of the pH sensitivecompound alone and a leakage of the amphipathic substance alone.

It will be noted that to satisfy (1) and (2) above means to satisfy bothof the following relations of leakage Lc of a pH sensitive carrier(complex of a pH sensitive compound and an amphipathic substance), La ofthe pH sensitive compound alone and Lb of the amphipathic substance.More particularly, (1) above is represented by the following formula(1), and (2) above is represented by the following formula (2). In thefollowing formulas, leakages at a pH of 7.4 are, respectively,represented by Lc_(7.4), La_(7.4) and Lb_(7.4), and leakages at a pH of5.0 or 4.5 are, respectively, represented by Lc_(x), La_(x) and Lb_(x).

Δ=(Lc _(x) −Lc _(7.4))−(La _(x) −La _(7.4))>0  Formula (1)

Δ′=Lc _(x)−(La _(x) +Lb _(x))>0  Formula (2)

The results are shown in Tables 2 to 7. It will be noted that therespective values indicated in Tables 2 to 7 are an average value ofthree measurements and ± is SD.

Furthermore, 1600 nmol (663 μg) of deoxycholic acid and differentweights of macromolecular materials were used to prepare particles,followed by evaluating the occurrence of leakage at a pH of 5.0. In FIG.10, there are shown the results of leakage of the complexes ofdeoxycholic acid and macromolecular materials at a pH of 5.0. It will benoted that the values in FIG. 10 are those values of one measurement,respectively.

TABLE 3 Functional evaluation of particles prepared using a variety ofamphipathic substances Deoxycholate Hydrophobic Hydrophobic complexedparticle material only material Leakage (%) Leakage (%) Castor oil pH7.4 2.2 ± 0.4 4.4 ± 0.6 pH 5.0 14.5 ± 0.2  7.3 ± 0.3 PEG10- pH 7.4 2.3 ±0.3 1.2 ± 0.7 castor oil pH 5.0 26.0 ± 0.4  3.4 ± 0.6 PEG10- pH 7.4 0.7± 0.4 0.3 ± 0.2 hardened pH 5.0 14.6 ± 1.1  2.9 ± 0.2 castor oil PEG40-pH 7.4 0.1 ± 0.1 0.6 ± 0.3 hardened pH 5.0 6.0 ± 0.5 3.1 ± 0.5 castoroil PEG60- pH 7.4 1.0 ± 0.6 0.7 ± 0.6 hardened pH 5.0 5.3 ± 0.8 2.5 ±0.6 castor oil SPAN 20 pH 7.4 4.9 ± 0.3 5.7 ± 0.7 pH 5.0 21.0 ± 0.6 10.1 ± 0.4  SPAN 40 pH 7.4 24.0 ± 1.9  14.9 ± 0.8  pH 5.0 50.4 ± 3.7 20.8 ± 1.4  SPAN 60 pH 7.4 5.1 ± 0.4 7.9 ± 0.3 pH 5.0 36.0 ± 1.4  17.5 ±0.4  SPAN 80 pH 7.4 3.9 ± 0.1 5.1 ± 0.5 pH 5.0 27.8 ± 0.7  10.0 ± 0.7 

TABLE 2 Functional evaluation of particles prepared using a variety ofamphipathic substances Deoxycholate Hydrophobic Hydrophobic complexedparticle material only material Leakage (%) Leakage (%) Deoxycholate pH7.4  1.0 ± 0.2 — only pH 5.0 14.6 ± 0.6 — Tween 20 pH 7.4 61.5 ± 2.159.5 ± 1.8  pH 5.0 80.2 ± 3.4 61.9 ± 0.5  Tween 40 pH 7.4  8.9 ± 0.2 7.9± 0.5 pH 5.0 40.0 ± 0.3 9.8 ± 0.7 Tween 60 pH 7.4  2.9 ± 0.1 2.4 ± 0.2pH 5.0 29.6 ± 0.5 6.3 ± 0.2 Tween 80 pH 7.4  7.0 ± 0.8 7.3 ± 0.1 pH 5.035.7 ± 1.0 10.8 ± 0.4  Tween 65 pH 7.4  7.5 ± 0.4 7.1 ± 0.7 pH 5.0 16.4± 0.6 8.3 ± 0.7 Tween 85 pH 7.4  5.8 ± 0.2 5.1 ± 0.7 pH 5.0 15.1 ± 0.66.3 ± 0.2 PEG 20 pH 7.4 69.5 ± 3.8 70.3 ± 2.2  stearyl ether pH 5.0 78.3± 0.7 72.0 ± 3.1  PEG 23 pH 7.4  2.9 ± 0.2 2.0 ± 0.1 lauryl ether pH 5.013.3 ± 0.4 4.7 ± 0.6

TABLE 4 Functional evaluation of particles prepared using a variety ofamphipathic substances Deoxycholate complexed Hydrophobic Hydrophobicparticle material only material Leakage (%) Leakage (%) Ethyl oleate pH7.4 4.6 ± 0.3 7.9 ± 0.2 pH 5.0 22.1 ± 0.1  11.2 ± 1.3  Ethyl octanoatepH 7.4 3.0 ± 0.3 9.0 ± 1.0 pH 5.0 19.3 ± 1.2  11.1 ± 1.1  Ethyl lauratepH 7.4 5.0 ± 0.5 8.7 ± 0.9 pH 5.0 23.2 ± 5.5  11.9 ± 1.2  L-Phenyl- pH7.4 3.4 ± 0.5 7.9 ± 0.5 alanine pH 5.0 18.8 ± 1.0  10.7 ± 0.4  L-LeucinepH 7.4 1.2 ± 0.8 7.3 ± 0.2 pH 5.0 17.6 ± 0.5  13.2 ± 3.7  L-Histidine pH7.4 0.5 ± 0.1 6.7 ± 0.4 pH 5.0 15.2 ± 0.9  8.9 ± 0.5 Soybean oil pH 7.42.1 ± 0.3 7.2 ± 0.1 pH 5.0 17.6 ± 0.3  9.3 ± 0.2 Tricaproin pH 7.4 3.0 ±0.9 6.9 ± 0.9 pH 5.0 17.6 ± 3.4  8.4 ± 0.9 Tricaprylin pH 7.4 1.6 ± 0.46.8 ± 0.9 pH 5.0 16.4 ± 1.9  9.0 ± 1.1

TABLE 5 Functional evaluation of particles prepared using a variety ofamphipathic substances Deoxycholate complexed Hydrophobic Hydrophobicparticle material only material Leakage (%) Leakage (%) SPAN 65 pH 7.43.0 ± 0.2 4.2 ± 0.4 pH 5.0 46.6 ± 1.5  13.0 ± 0.3  SPAN 85 pH 7.4 7.0 ±0.6 5.2 ± 0.4 pH 5.0 78.7 ± 1.2  17.7 ± 1.2  1-Butanol pH 7.4 2.7 ± 0.78.8 ± 0.1 pH 5.0 18.6 ± 0.7  11.1 ± 0.5  1-Octanol pH 7.4 3.0 ± 0.7 9.0± 0.3 pH 5.0 19.2 ± 1.2  11.7 ± 0.1  1-Dodecanol pH 7.4 2.7 ± 0.7 7.9 ±0.2 pH 5.0 14.1 ± 0.6  9.1 ± 0.8 1-Hexa- pH 7.4 6.9 ± 0.3 9.0 ± 0.9dodecanol pH 5.0 24.0 ± 1.0  11.0 ± 0.5  1-Eicosanol pH 7.4 2.8 ± 0.37.6 ± 0.4 pH 5.0 20.8 ± 2.1  8.6 ± 0.5 Lauric acid pH 7.4 1.8 ± 0.2 6.2± 0.4 pH 5.0 17.0 ± 1.0  14.2 ± 0.4  Oleic acid pH 7.4 4.0 ± 0.5 2.2 ±0.1 pH 5.0 87.2 ± 5.9  76.0 ± 2.3 

TABLE 6 Functional evaluation of particles prepared using a variety ofamphipathic substances Deoxycholate complexed Hydrophobic Hydrophobicparticle material only material Leakage (%) Leakage (%) Benzyl benzoatepH 7.4 0.6 ± 0.1 7.3 ± 2.0 pH 5.0 11.8 ± 1.0  9.7 ± 0.5 Propyl para- pH7.4 0.5 ± 0.1 5.4 ± 0.2 oxybenzoate pH 5.0 14.0 ± 0.4  7.9 ± 0.1Ascorbyl pH 7.4 0.5 ± 0.4 1.7 ± 0.1 palmitate pH 5.0 11.7 ± 0.7  9.9 ±1.0 Cyclo- pH 7.4 1.6 ± 0.2 6.3 ± 0.6 dextrin pH 5.0 16.4 ± 0.9  9.0 ±0.7 Cholesterol pH 7.4 1.9 ± 0.2 4.8 ± 0.1 pH 5.0 15.0 ± 0.2  7.6 ± 0.5Lactose pH 7.4 1.3 ± 0.1 6.1 ± 0.2 pH 5.0 18.3 ± 0.4  8.9 ± 0.2 SqualenepH 7.4 1.3 ± 0.2 5.4 ± 0.4 pH 5.0 18.6 ± 1.4  9.0 ± 0.5 Squalane pH 7.40.9 ± 0.2 7.8 ± 0.6 pH 5.0 20.9 ± 0.7  9.4 ± 0.5 α-Toco- pH 7.4 5.7 ±0.8 5.4 ± 0.2 pherol pH 5.0 39.5 ± 6.4  8.8 ± 0.6 α-Toco- pH 7.4 1.0 ±0.3 5.9 ± 0.2 pherol pH 5.0 18.0 ± 1.0  7.0 ± 2.1 acetate

TABLE 7 Functional evaluation of particles prepared using a variety ofamphipathic substances Deoxycholate complexed Hydrophobic Hydrophobicparticle material only material Leakage (%) Leakage (%) Monocaprin pH7.4  1.2 ± 0.6 4.0 ± 2.6 pH 5.0 13.9 ± 0.8 8.1 ± 0.2 Monocaprylin pH 7.4 0.8 ± 0.5 4.9 ± 1.8 pH 5.0 14.6 ± 0.7 8.5 ± 0.4 Monolaurin pH 7.4  3.1± 0.5 3.6 ± 0.3 pH 5.0 14.3 ± 0.6 5.6 ± 0.4 Monomyristin pH 7.4  4.0 ±0.6 3.8 ± 0.3 pH 5.0 13.5 ± 0.4 5.4 ± 0.1 Monopalmitin pH 7.4  6.9 ± 0.67.8 ± 2.5 pH 5.0 19.3 ± 0.4 8.1 ± 0.7 Monostearin pH 7.4  7.0 ± 0.6 7.9± 1.0 pH 5.0 23.8 ± 0.8 9.6 ± 0.6 Monoolein pH 7.4 38.4 ± 3.0 6.3 ± 0.4pH 5.0 71.3 ± 2.1 8.3 ± 0.4 Glycerol pH 7.4  6.2 ± 0.3 8.0 ± 0.2distearate pH 5.0 28.4 ± 1.6 11.0 ± 1.4  Glycerol pH 7.4  8.0 ± 0.4 7.2± 0.5 dioleate pH 5.0 24.1 ± 0.7 7.4 ± 0.6 α,α pH 7.4 11.0 ± 1.6 7.6 ±1.0 Dilaurin pH 5.0 25.3 ± 1.1 7.4 ± 0.6

From the above investigation, it has been shown that appropriatesubstances are those including: Tween 20, Tween 40, Tween 60 and Tween80, which are polyoxyethylene sorbitan monofatty acid esters having 12to 18 carbon atoms; SPAN 40, SPAN 60, SPAN 80, SPAN 65 and SPAN 85,which are sorbitan fatty acid esters having 16 to 18 carbon atoms;glycerol derivatives such as glycol monooleate (monoolein in the table),glycerol distearate, glycerol dioleate and glycerol dilaurate (α,αdilaurin); PEG-10-castor oil which is polyoxyethylene castor oil; andα-tocopherol. It will be noted that the “number of carbon atoms” of theamphipathic substance means the number of carbon atoms of a fatty acidmoiety (acyl group) serving as the hydrophobic site of the amphipathicsubstance.

(8) Investigation of the Ratio of Amphipathic Substance

The investigation of (7) above revealed amphipathic substances which arecapable of bringing about the development of the effect and thosesubstances which are not. Next, it was checked what ratio of a substancecapable of bringing about the development of the effect was necessary torealize the development of the effect. EYPC was chosen as a substancenot bringing about the development of the effect and DLPC or SPAN 85 wasmixed with EYPC at different ratios to make a total of 1000 nmol andcarriers made of a plurality of amphipathic substances were prepared.

DLPC or SPAN 85 was mixed with EYPC at different ratios to make a totalof 1000 nmol, followed by complexing with 1600 nmol of deoxycholic acidto prepare carriers. The respective carriers were subjected to aleaching test at pHs of 7.4 and 5.0 to check the effect development.

FIG. 11 shows the leakage of each of the complexes of EYPC, deoxycholicacid and DLPC or SPAN 85 at a pH of 7.4 in (A) and at a pH of 5.0 in(B). The respective values in FIGS. 11(A) and (B) are an average valueof three different measurements and ± is SD.

When the ratio of DLPC or SPAN 85:EYPC (mol:mol) is within the range of100:150 to 100:0, the pH sensitive leakage was confirmed (FIGS. 11(A)and (B)). It was thus revealed that in order to obtain a pH sensitivecarrier capable of developing the effect in a weakly acidic environmentas a result of complexing with deoxycholic acid, the ratio of anappropriate type of amphipathic substance was desirably within such arange as indicated above.

(9) Research of pH Sensitive Compounds Other than Deoxycholic Acid

From the above results, it was found that deoxycholic acid affected thestate of hydrophobic association in a weakly acidic environment. Thus,it will be expected that molecules having structures analogous todeoxycholic acid likewise can provide a pH sensitive carrier. Then,there were selected, as an analogous molecule of deoxycholic acid, avariety of bile acids, glycyrrhizic acid and glycyrrhetinic acid,followed by carrying out a leaching test and a membrane fusion test ofcomplexes of the above acids and DLPC to check whether they could beusable as a pH sensitive compound.

1000 nmol of DLPC and 1600 nmol of a variety of acids (hereinafterreferred to as candidate compounds) were used to prepare carriers.

FIG. 12 shows leakages of complexes of DLPC and a variety of candidatecompounds at a pH of 7.4 in (A) and a pH of 5.0 in (B). The respectivevalues in FIG. 12 are an average value of three different measurementsand ± is SD.

In FIG. 13, there is shown a graph showing leakages of complexes of DLPCand a variety of candidate compounds at different pHs. The respectivevalues in FIG. 13 are an average value of three different measurementsand ± is SD.

FIG. 14 shows the fusion rates of (A) a variety of pH sensitivecompounds alone and (B) complexes of DLPC and a variety of pH sensitivecompounds at a pH of 7.4 and a pH of 5.0. The respective values are anaverage value of three different measurements and ± is SD.

The carriers prepared from all the candidate compounds did not causeleakage at a pH of 7.4, whereas at a pH of 5.0, the carriers prepared byuse of deoxycholic acid, cholic acid, ursodeoxycholic acid,chenodeoxycholic acid, hyodeoxcholic acid, C27 bile acid(trihydroxycholestanoic acid), glycodeoxycholic acid, glycyrrhizic acidand glycyrrhetinic acid significantly caused a greater leakage than withthe cases wherein the candidate compounds alone were added, therebyshowing a membrane disruptive function promoting effect (FIGS. 12(A) and(B)). It was confirmed that these carriers also had a pH sensitivemembrane fusion function promoting effect (FIGS. 14(A) and (B)). In viewof the results in FIGS. 5(A) and 5(B), it was shown that theillustrative carriers developed the fusion function promoting effectalong with the membrane disruptive function promoting effect.

When the pH profile of these carriers was checked, it was found that thepH at which leakage started differed depending on the type of moleculeused (FIG. 13). It is theorized that the pKa differs and the manner offorming association with an amphipathic substance differs, bothdepending on the type of molecule. These results reveal that it ispossible to select in detail a pH at which the effect develops. Thus, itcan be expected to enable detailed settings of in vivo delivery andintracellular delivery. According to this test, it was elucidated thatthese pH sensitive carriers had the effects at a pH of 7 to 3.

(10) Investigation of the Combinations of pH Sensitive Compounds andAmphipathic Substances

The presence or absence of the effect development was confirmed andchecked with respect to many combinations of the compounds (pH sensitivecompounds) having analogous structures to deoxycholic acid anddetermined in FIGS. 12(A) and (B), FIG. 13 and FIGS. 14(A) and (B) toyield the development of the effect and the amphipathic substancesdetermined by the screening in Tables 2 to 7 and in FIG. 10 to bringabout the development of the effect.

Carriers were prepared using 1000 nmol of an amphipathic substance and100 nmol of a pH sensitive compound, or 1000 nmol of an amphipathicsubstance and 6400 nmol of a pH sensitive compound. In Tables 8 and 9,there are shown the results of the leaching test of a variety ofcomplexes of pH sensitive compounds and amphipathic substances.

TABLE 8 Evaluation of functional carriers obtained by combinations of pHsensitive compounds (100 nmol) and amphipathic substances (1000 nmol)(leaching test) (n = 1 in the test) Deoxycholic Ursodeoxy- Chenoxy-Hyodeoxy- Glycodeoxy- Glycyrrhizic acid Cholic acid cholic acid cholicacid cholic acid cholic acid acid Δ Δ′ Δ Δ′ Δ Δ′ Δ Δ′ Δ Δ′ Δ Δ′ Δ Δ′DLPC 1.3 3.1 1.4 2.8 1.2 2.3 3.6 3.8 0.9 1.1 1.0 0.1 4.9 3.9 DDPC 49.445.9 12.8 7.7 9.4 5.3 51.2 47.7 27.8 23.8 12.6 8.7 58.6 42.9 Tween 201.3 13.8 2.9 14.4 2.8 21.5 5.2 20.7 5.3 13.5 2.0 7.6 12.8 17.5 Tween 401.3 10.8 3.0 10.0 2.1 8.0 1.8 8.0 1.3 4.4 0.6 5.4 5.0 7.9 Tween 60 2.14.9 2.2 4.3 2.5 4.0 2.4 4.3 0.6 2.5 1.2 3.4 6.9 4.9 Tween 80 1.0 6.4 1.76.8 2.3 1.7 2.1 3.5 1.2 1.9 1.2 4.2 11.7 5.5 PEG 10 castor 1.0 3.4 2.92.9 3.7 4.4 2.2 5.4 1.5 2.3 0.9 2.0 3.6 11.0 oil SPAN 40 7.5 16.7 7.518.7 6.4 16.9 7.8 17.3 3.8 7.2 7.3 12.3 3.0 6.8 SPAN 60 12.6 15.8 18.415.5 11.9 15.2 14.1 13.4 10.4 11.4 13.6 13.5 3.7 8.1 SPAN 80 8.8 13.16.0 5.6 1.5 3.4 3.0 5.5 2.8 3.3 18.6 22.9 3.9 10.0 SPAN 65 3.3 3.1 4.43.9 16.2 13.6 6.7 6.3 12.8 11.0 4.4 1.5 2.4 0.8 SPAN 85 10.4 10.4 6.46.2 4.2 5.1 5.6 7.0 2.9 3.6 1.3 2.9 1.5 2.8 α-Tocopherol 10.4 23.5 4.020.2 3.1 4.5 3.3 6.3 1.7 4.3 1.7 5.1 2.1 4.8 Monoolein 4.0 4.6 2.8 3.71.8 3.3 2.4 3.4 0.4 2.0 11.6 17.0 3.5 2.8 Glycerol 2.5 4.6 2.4 4.1 3.24.7 2.9 4.8 3.2 3.9 4.2 3.0 1.8 2.6 distearate Glycerol 5.0 4.9 3.0 4.42.1 3.5 3.4 3.5 2.6 1.5 3.8 3.0 3.7 2.6 dioleate α,α dilaurin 4.1 10.23.6 5.9 1.5 3.2 2.3 3.1 1.2 0.6 3.8 4.8 2.0 1.4 Δ = (Lc_(4.5) −Lc_(7.4)) − (La_(4.5) − La_(7.4)) Δ′ = Lc_(4.5) − (La_(4.5) + Lb_(4.5))Lc_(pH): a leakage of a complex of a pH sensitive compound and anamphipathic substance at a given pH La_(pH): a leakage of a pH sensitivecompound alone at a given pH Lb_(pH): a leakage of an amphipathicsubstance at a given pH

TABLE 9 Evaluation of functional carriers obtained by combinations of pHsensitive compounds (6400 nmol) and amphipathic substances (1000 nmol)(leaching test) (n = 1 in the test) Deoxycholic Ursodeoxy- Chenoxy-Hyodeoxy- Glycodeoxy- Glycyrrhizic acid Cholic acid cholic acid cholicacid cholic acid cholic acid acid Δ Δ′ Δ Δ′ Δ Δ′ Δ Δ′ Δ Δ′ Δ Δ′ Δ Δ′DLPC 71.5 80.4 44.3 49.3 64.2 57.8 46.2 62.0 8.0 11.7 49.9 52.2 62.561.0 DDPC 25.2 54.4 34.1 67.1 35.5 60.9 *5.3 9.9 34.3 63.9 41.7 64.743.4 66.6 Tween 20 2.5 21.6 7.2 14.2 16.8 22.6 *3.7 17.6 16.9 32.8 9.028.0 15.0 26.8 Tween 40 47.8 51.9 16.3 27.3 46.5 45.3 14.7 57.8 70.478.0 5.5 16.6 31.9 36.6 Tween 60 65.2 67.6 3.0 7.2 46.9 43.2 31.2 59.285.1 90.8 4.3 7.8 55.2 57.1 Tween 80 58.0 63.4 10.6 16.9 50.6 43.3 22.952.4 77.2 83.5 8.6 15.0 49.4 49.6 PEG 10 castor 74.1 77.3 4.5 12.8 12.67.4 36.3 56.5 57.5 61.6 4.9 7.6 24.7 24.0 oil SPAN 40 75.1 70.2 13.540.2 8.6 3.5 38.9 52.3 2.2 13.9 16.7 11.0 4.4 6.7 SPAN 60 74.9 70.0 34.139.9 16.5 6.3 33.8 47.5 7.5 10.5 13.1 8.0 8.3 3.1 SPAN 80 72.8 71.7 31.260.2 9.2 2.4 32.0 47.0 25.9 27.2 6.2 2.0 6.6 4.0 SPAN 65 72.6 66.1 33.835.7 38.0 24.6 27.3 49.2 6.7 4.3 12.5 6.3 17.4 8.3 SPAN 85 73.8 70.948.2 56.6 13.1 4.5 31.9 43.4 33.0 33.5 6.6 2.9 22.8 16.9 α-Tocopherol69.8 69.0 7.9 27.2 5.0 1.1 6.2 16.0 22.4 22.7 5.7 2.2 7.1 7.0 Monoolein40.7 59.0 31.0 39.5 9.7 2.4 16.9 42.8 34.7 37.4 2.0 11.3 8.2 36.7Glycerol 78.1 73.3 10.9 18.2 22.0 14.0 32.3 57.5 3.9 7.4 6.2 1.4 49.042.2 distearate Glycerol 75.6 72.4 8.4 28.6 11.8 2.0 31.3 41.0 29.7 30.010.5 6.0 6.5 1.3 dioleate α,α dilaurin 61.7 61.0 15.9 42.7 12.7 2.3 29.543.3 38.8 44.2 16.7 18.9 50.6 57.9 Δ = (Lc_(4.5) − Lc_(7.4)) − (La_(4.5)− La_(7.4)) Δ′ = Lc_(4.5) − (La_(4.5) + Lb_(4.5)) Lc_(pH): a leakage ofa complex of a pH sensitive compound and an amphipathic substance at agiven pH La_(pH): a leakage of a pH sensitive compound alone at a givenpH Lb_(pH): a leakage of an amphipathic substance at a given pH As tothe combinations marked by *, the results of the test based on 30minutes incubation are shown.

From Tables 8 and 9, it has been found that for any of the combinations,Δ and Δ′, which are indices for having a significant effect, provideplus values, respectively, the carriers obtained from the combinationsof Tables 8 and 9 have a pH sensitive function.

(11) Confirmation of Membrane Fusion Against Cell Membrane

From the results of the foregoing (3), (5), (6), (9) and the like, ithas been shown that an illustrative pH sensitive carrier develops themembrane disruptive function promoting effect and membrane fusionfunction promoting effect in a weakly acidic environment. Fusion betweena pH sensitive carrier and a cell membrane was confirmed. In moredetail, a fluorescence-labeled pH sensitive carrier and HeLa cells weresubjected to short time incubation in media adjusted to pHs of 7.4 and5.3, respectively, and staining of a cell surface membrane was checkedthereby confirming the fusion between the pH sensitive carrier and thecell membrane.

As a result, the fluorescence was observed as a point of origin or in aregion close to the nucleus at a pH of 7.4 (FIG. 15(A)). This indicatesthat the pH sensitive carrier is taken up by the cells and exists in theendosome and lysosome. It will be noted that a similar image as observedas with the case of a fluorescence-labeled amphipathic substance alone(data not shown).

On the other hand, there was observed an image wherein the shape offluorescence and the shape of the cell coincided with each other in theentire visual field at a pH of 5.3 (FIG. 15(B)). It is theorized thatthe fluorescence-labeled pH sensitive carrier underwent membrane fusionwith the cell membrane on the cell surface, for which the fluorescencespread in the form of cell.

From the above results, it has been revealed that the pH sensitivecarrier develops a membrane fusion function promoting effect a weaklyacidic environment in the medium and undergoes membrane fusion with thecell membrane on the cell surface.

When the cell fluorescence intensity was evaluated by use of a flowcytometer, the incubated cells showed a great fluorescence intensity ata pH of 5.3 (FIG. 15(C)). It is considered that the results rely on thefluorescence-labeled pH sensitive carrier undergoing membrane fusion inlarge amounts. Thus, it has been shown that the pH sensitive carrier isable to undergo membrane fusion with an actual cell membrane in anefficient manner.

(12) Influence of the Incorporation of a Peptide and a Protein on theEffect Development

It has been investigated to incorporate a peptide or a protein havingphysiological activity through hydrophobic association for use as DDS.This seems to be a promising method of the present carrier. Hence,influences of the incorporation of physiologically active substances onthe effect development of the carrier were checked using OVA 257-264(SIINFEKL, purchased from PH Japan) as a model peptide and OVA(purchased from Sigma-Aldrich Co. LLC.) as a model protein.

Initially, in order to evaluate the incorporation of the physiologicallyactive substance, the particle size and polydispersity index (PDI) of acarrier where the peptide or protein (192 μg) was incorporated in aDLPC-deoxycholate complex (1000 nmol:1600 nmol) were measured (Table10).

Next, the leakages of the carriers incorporated with different amountsof peptide (A) or protein (B) relative to 1000 nmol of DLPC and 1600nmol of deoxycholate acid were determined. In FIG. 16, the results ofleakages of (A) peptide and (B) protein-containing carriers at pHs of7.4 and 5.0 are shown. The values in FIG. 16 are each an average valueof three different measurements and ± is SD.

Moreover, the fusion rate of each of the carriers incorporated with 768μg of the peptide or protein relative to 1000 nmol of DLPC and 1600 nmolof (A) deoxycholic acid or (B) ursodeoxycholic acid was checked. In FIG.17, there are shown the results of the fusion rates of (A) deoxycholicacid and (B) ursodeoxycholic acid at pHs of 7.4 and 5.0. The values inFIGS. 17(A) and (B) are each an average value of three differentmeasurements and ± is SD.

TABLE 10 Particle size and PDIs. DLPC-deoxy Diameter (nm) PDI Micelleonly 43.3 ± 0.3 0.09 ± 0.01 peptide 56.0 ± 0.9 0.21 ± 0.01 OVA-protein71.6 ± 0.5 0.04 ± 0.02 The value is an average as a result of fivemeasurements and ± is SD. Micelle only: DLPC-deoxycholate complex alonepeptide: peptide-containing DLPC-deoxycholate complex OVA-protein:OVA-containing DLPC-deoxycholate complex

The incorporation of the peptide or protein in the carrier had atendency to slightly increase the particle size of the carrier (Table10). Thus, it was suggested that these substances were incorporated inthe carrier. On the other hand, as to the leakage being caused, thevalues were the same as those obtained in the case of no incorporationin any amounts of the peptide or protein (FIGS. 16(A) and (B)) and itwas shown that no lowering of the effect of the carrier was caused owingto the incorporation of the peptide or protein.

With respect to the results of the fusion test, similar results wereobtained (FIGS. 17(A) and (B)). From these results, it was revealed thatthe incorporation of the physiologically active substance did notgreatly affect the effect development of the carrier.

(13) Delivery to Cellular Cytosol 1

Many reports have been made on carriers, which have such properties asto promote membrane fusion and membrane disruption in a weakly acidicenvironment and which enables an included or incorporated substance todeliver via an endosome to a cellular cytosol. An attempt was made todeliver a physiologically active substance to a cellular cytosol by useof a formulated pH sensitive carrier.

A carrier was prepared using 140 μg/mL of a fluorescence-labeled peptidesolution relative to 1000 nmol of DLPC and 1600 nmol of deoxycholic acidor ursodeoxycholic acid. For a control, a carrier was prepared using 140μg/mL of a fluorescence-labeled peptide solution relative to 1000 nmolof DLPC. In FIG. 18, there is shown a photograph of (A) a solution of afluorescence-labeled peptide alone, (B) a solution of afluorescence-labeled peptide-containing DLPC alone, (C) a solution of afluorescence-labeled peptide-containing DLPC-deoxycholate complex, and(D) a solution of a fluorescence-labeled peptide-containingDLPC-ursodeoxycholate complex.

The solution (B) of the fluorescence-labeled peptide-containing DLPC,the solution (C) of the fluorescence-labeled peptide-containingDLPC-deoxycholate complex, and the solution (D) of thefluorescence-labeled peptide-containing DLPC-ursodeoxycholate complexbecame weakly fluorescent over the solution (A) of thefluorescence-labeled peptide alone. This is due to thefluorescence-labeled peptide being fixed to the hydrophobic domains ofthe carrier, thus suggesting that the fluorescence-labeled peptide isincorporated in the carrier.

Next, the delivery of a fluorescence-labeled peptide to the cellularcytosol was attempted. More particularly, 100 μL of each of thefluorescence-labeled peptide-containing samples (A) to (D) describedabove (14 μg of the fluorescence-labeled peptide/well) was administeredinto the RAW cells cultured in 1900 μL of a 10% FBS-containing MEMmedium and taken up in overnight. The cells were rinsed and subjected tothree hours post-incubation, followed by observation of the cellsthrough a fluorescence microscope.

In FIG. 19, there are shown fluorescence microphotographs of (A) thefluorescence-labeled peptide alone, (B) the fluorescence-labeledpeptide-containing DLPC alone, and (C) the fluorescence-labeledpeptide-containing DLPC-deoxycholate complex. In FIG. 20, there areshown (A) a microphotograph and (B) a fluorescence microphotograph ofthe fluorescence-labeled peptide-containing DLPC-deoxycholate complex,and (C) a microphotograph and (D) a fluorescence microphotograph of thefluorescence-labeled peptide-containing DLPC-ursodeoxycholate complex.

With the case of the fluorescence-labeled peptide alone (A) or thefluorescence-labeled peptide-containing DLPC alone, most of fluorescencewas seen as a point of origin, indicating that the fluorescence-labeledpeptide remained in the endosome (FIGS. 19(A) and (B)).

On the other hand, with respect to the DLPC-deoxycholate complex (C)incorporated with a fluorescence-labeled peptide, fluorescence wasconfirmed in substantially all the cells throughout the cell, indicatingthat the fluorescence-labeled peptide escaped from the endosome andmigrated to the cytosol (FIG. 19(C)). Since the carrier was chargednegatively and the post incubation was carried out for three hours, itis difficult to consider that this fluorescence is an image obtained byadsorption of the carrier over the entire surface of the cell, but it isconsidered that the fluorescence-labeled peptide is delivered to thecytosol via the endosome.

With respect to the carrier prepared by use of ursodeoxycholic acid, thefluorescence was observed throughout the cellular cytosol as in the caseof deoxycholic acid, and efficient cytosolic delivery was confirmed(FIGS. 20(C) and (D)).

From the foregoing, it was shown that the illustrative pH sensitivecarriers enable efficient cytosolic delivery of a physiologically activesubstance.

(14) Delivery to Cellular Cytosol 2

Subsequently, an attempt was made to deliver a protein to a cellularcytosol. β-gal was chosen as a model protein and incorporated in a pHsensitive carrier. The delivery to the cellular cytosol was evaluated byvisualizing enzymatic activity after application to RAW cells andcomparing the activities.

Carriers were prepared using 1.4 mg/mL of a β-gal solution relative to1000 nmol of DLPC and 1600 nmol of deoxycholic acid or ursodeoxycholicacid.

In FIG. 21, there are shown microphotographs of (A) β-gal alone, (B) aβ-gal-containing DLPC-deoxycholate complex and (C) a β-gal-containingDLPC-ursodeoxycholate complex.

The cells to which β-gal alone had been added were not stained (FIG.21(A)). This is due to the β-gal being decomposed in the endosome,indicating no migration to the cellular cytosol. On the other hand, withthe case of the incorporation in the pH sensitive carriers, bluestaining with β-gal was confirmed (FIGS. 21(B) and (C)), indicating thatβ-gal escaped from the endosome and migrated to the cellular cytosolwhile keeping enzymatic activity. According to Vincent M. Rotello etal., J. Am. Chem. Soc. 2010 132(8) 2642-2645, a similar experiment isconducted for the purpose of cytosolic delivery of β-gal and similarresults as in the above literature are obtained herein, thus supportingthe above discussion.

(15) Delivery to Cellular Cytosol 3

In (13) and (14) above, delivery of a physiologically active substancesupported with a pH sensitive carrier was confirmed. Next, an attemptwas made to deliver to cellular cytosol when a pH sensitive carrier anda physiologically active substance were respectively independently used.Where a pH sensitive carrier and a physiologically active substance weretaken up in the same endosome, the endosome underwent membranedisruption by the membrane disruptive function promoting effect of thepH sensitive carrier. On this occasion, it is considered that thephysiologically active substance mixed in the endosome is leached outfrom the endosome and can be delivered to the cellular cytosol.

With the case where fluorescence-labeled peptide-FITC was added to RAWcells and also with the case where fluorescence-labeled OVA-FITC wasadded to RAW cells, the fluorescence in the cell was confirmed as apoint of origin, indicating that the fluorescence-labeled peptide-FITCand the fluorescence-labeled OVA-FITC, respectively, remained in theendosome (FIG. 22A (A) and (B)).

Next, the EYPC-deoxycholate complex, in which the membrane disruptionpromoting function and membrane fusion promoting function had not beenobserved in the foregoing (3) and (5), were used in combination with thefluorescence-labeled peptide-FITC or the fluorescence-labeled OVA-FITC.More particularly, a solution of EYPC-deoxycholate complex was furtheradded to a culture solution of RAW cells containing thefluorescence-labeled peptide-FITC. Separately, a solution ofEYPC-deoxycholate complex was further added to a culture solution of RAWcells containing the fluorescence-labeled OVA-FITC. In these cases, thefluorescence in the cells was confirmed as a point of origin like theabove case, indicating that the fluorescence-labeled peptide-FITC andthe fluorescence-labeled OVA-FITC, respectively, remained in theendosome (FIG. 22A (C) and (D)).

Next, a pH sensitive carrier was used in combination with thefluorescence-labeled peptide-FITC or the fluorescence-labeled OVA-FITC.More particularly, a solution of a pH sensitive carrier having amembrane disruptive function promoting effect was further added to aculture solution of RAW cells containing the fluorescence-labeledpeptide-FITC. In addition, a solution of a pH sensitive carrier having amembrane disruptive function promoting effect was further added to aculture solution of RAW cells containing the fluorescence-labeledOVA-FITC. For the pH sensitive carrier, there were usedDLPC-deoxycholate complex, SPAN 80-deoxycholate complex,DDPC-deoxycholate complex, polyoxyethylene castor oil (PEG-10 castoroil)-deoxycholate complex, Tween 20-deoxycholate complex, Tween80-deoxycholate complex, α-tocopherol-deoxycholate complex,DLPC-ursodeoxycholate complex, DLPC-glycyrrhizic acid complex,DLPC-chenodeoxycholate complex, DLPC-hyodeoxycholate complex, andDLPC-glycodeoxycholate complex. The respective pH sensitive carrierswere prepared using 160 nmol of a pH sensitive compound and 100 nmol ofan amphipathic substance. In these cases, fluorescence was recognizedthroughout the cellular cytosol (FIG. 22A (E) to (J), FIG. 22B (K) to(T) and FIG. 22C (U) to (AB)). Accordingly, it was shown that even whena physiologically active substance was used independently of pHsensitive carriers having a membrane disruptive function promotingeffect (not supported), delivery to cellular cytosol could be made.

What is claimed is:
 1. A pH sensitive carrier which comprises: at leastone pH sensitive compound selected from the group consisting ofdeoxycholic acid, cholic acid, ursodeoxycholic acid, chenodeoxycholicacid, hyodeoxycholic acid, C27 bile acid, glycodeoxycholic acid,glycyrrhizic acid, glycyrrhetinic acid and salts thereof; and at leastone amphipathic substance selected from the group consisting of aphosphatidylcholine having 10 to 12 carbon atoms, a polyoxyethylenesorbitan monofatty acid ester having 12 to 18 carbon atoms, a sorbitanfatty acid ester having 16 to 18 carbon atoms, glycerol monooleate,glycerol dilaurate, glycerol distearate, glycerol dioleate,polyoxyethylene castor oil and α-tocopherol, and which is capable ofdeveloping a membrane disruptive function promoting effect.
 2. The pHsensitive carrier as defined in claim 1, wherein the pH sensitivecompound and the amphipathic substance form micellar particles.
 3. ThepH sensitive carrier as defined in claim 2, wherein the particle size is10 to 200 nm.
 4. The pH sensitive carrier as defined in claim 1, whereinthe pH sensitive compound is present in an amount of not less than 10moles per 100 moles of the amphipathic substance.
 5. The pH sensitivecarrier defined in claim 1, wherein when a leakage of the pH sensitivecompound alone in a leaching test is taken as La, a leakage of theamphipathic substance alone taken as Lb, a leakage of the pH sensitivecarrier taken as Lc, leakages at a pH of 7.4, respectively, taken asLc_(7.4), La_(7.4) and Lb_(7.4), and leakages at a pH of 5.0 or 4.5,respectively, taken as Lc_(x), La_(x) and Lb_(x), Δ represented by thefollowing formula (1) is not smaller than 5 and Δ′ represented by thefollowing formula (2) is not smaller than 5.Δ=(Lc _(x) −Lc _(7.4))−(La _(x) −La _(7.4))  Equation (1)Δ′=Lc _(x)−(La _(x) +Lb _(x))  Equation (2)
 6. A pH sensitive drugcomprising a pH sensitive carrier which includes at least one pHsensitive compound selected from the group consisting of deoxycholicacid, cholic acid, ursodeoxycholic acid, chenodeoxycholic acid,hyodeoxycholic acid, C27 bile acid, glycodeoxycholic acid, glycyrrhizicacid, glycyrrhetinic acid and salts thereof, and at least oneamphipathic substance selected from the group consisting of aphosphatidylcholine having 10 to 12 carbon atoms, a polyoxyethylenesorbitan monofatty acid ester having 12 to 18 carbon atoms, a sorbitanfatty acid ester having 16 to 18 carbon atoms, glycerol monooleate,glycerol dilaurate, glycerol distearate, glycerol dioleate,polyoxyethylene castor oil and α-tocopherol, and which is capable ofdeveloping a membrane disruptive function promoting effect, the pHsensitive carrier supporting a physiologically active substancetherewith.
 7. The pH sensitive drug as defined in claim 6, wherein thephysiologically active substance is made of a protein or peptide.
 8. ApH sensitive drug composition comprising: a pH sensitive carrier whichincludes at least one pH sensitive compound selected from the groupconsisting of deoxycholic acid, cholic acid, ursodeoxycholic acid,chenodeoxycholic acid, hyodeoxycholic acid, C27 bile acid,glycodeoxycholic acid, glycyrrhizic acid, glycyrrhetinic acid and saltsthereof, and at least one amphipathic substance selected from the groupconsisting of a phosphatidylcholine having 10 to 12 carbon atoms, apolyoxyethylene sorbitan monofatty acid ester having 12 to 18 carbonatoms, a sorbitan fatty acid ester having 16 to 18 carbon atoms,glycerol monooleate, glycerol dilaurate, glycerol distearate, glyceroldioleate, polyoxyethylene castor oil and α-tocopherol, and which iscapable of developing a membrane disruptive function promoting effect;and a physiologically active substance.
 9. The pH sensitive drugcomposition as defined in claim 8, wherein said physiologically activesubstance is made of a protein or peptide.
 10. A method for preparing apH sensitive carrier which is capable of developing a membranedisruptive function promoting effect, the method comprising associatingat least one pH sensitive compound selected from the group consisting ofdeoxycholic acid, cholic acid, ursodeoxycholic acid, chenodeoxycholicacid, hyodeoxycholic acid, C27 bile acid, glycodesoxycholic acid,glycyrrhizic acid, glycyrrhetinic acid and salts thereof, and at leastone amphipathic substance selected from the group consisting of aphosphatidylcholine having 10 to 12 carbon atoms, a polyoxyethylenesorbitan monofatty acid ester having 12 to 18 carbon atoms, a sorbitanfatty acid ester having 16 to 18 carbon atoms, glycerol monooleate,glycerol dilaurate, glycerol distearate, glycerol dioleate,polyoxyethylene castor oil and α-tocopherol.